Guide to Concrete Repair
ACI 546R-14
Reported by ACI Committee 546
First Printing
September 2014
ISBN: 978-0-87031-933-4
Guide to Concrete Repair
Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material
may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other
distribution and storage media, without the written consent of ACI.
The technical committees responsible for ACI committee reports and standards strive to avoid
ambiguities, omissions, and errors in these documents. In spite of these efforts, the users of ACI
documents occasionally find information or requirements that may be subject to more than one
interpretation or may be incomplete or incorrect. Users who have suggestions for the improvement of
ACI documents are requested to contact ACI via the errata website at http://concrete.org/Publications/
DocumentErrata.aspx. Proper use of this document includes periodically checking for errata for the most
up-to-date revisions.
ACI committee documents are intended for the use of individuals who are competent to evaluate the
significance and limitations of its content and recommendations and who will accept responsibility for
the application of the material it contains. Individuals who use this publication in any way assume all
risk and accept total responsibility for the application and use of this information.
All information in this publication is provided “as is” without warranty of any kind, either express or
implied, including but not limited to, the implied warranties of merchantability, fitness for a particular
purpose or non-infringement.
ACI and its members disclaim liability for damages of any kind, including any special, indirect, incidental,
or consequential damages, including without limitation, lost revenues or lost profits, which may result
from the use of this publication.
It is the responsibility of the user of this document to establish health and safety practices appropriate
to the specific circumstances involved with its use. ACI does not make any representations with regard
to health and safety issues and the use of this document. The user must determine the applicability of
all regulatory limitations before applying the document and must comply with all applicable laws and
regulations, including but not limited to, United States Occupational Safety and Health Administration
(OSHA) health and safety standards.
Participation by governmental representatives in the work of the American Concrete Institute and in
the development of Institute standards does not constitute governmental endorsement of ACI or the
standards that it develops.
Order information: ACI documents are available in print, by download, on CD-ROM, through electronic
subscription, or reprint and may be obtained by contacting ACI.
Most ACI standards and committee reports are gathered together in the annually revised ACI Manual of
Concrete Practice (MCP).
American Concrete Institute
38800 Country Club Drive
Farmington Hills, MI 48331
Phone: +1.248.848.3700
Fax:
+1.248.848.3701
www.concrete.org
ACI 546R-14
Guide to Concrete Repair
Reported by ACI Committee 546
John S. Lund, Chair
James Peter Barlow
Michael M. Chehab
Marwan A. Daye
Michael J. Garlich
Paul E. Gaudette
Timothy R. W. Gillespie
Yelena S. Golod
Fred R. Goodwin
Harald G. Greve
David W. Whitmore, Secretary
Ron Heffron
Robert F. Joyce
Lawrence F. Kahn
Brian F. Keane
Benjamin Lavon
Kenneth M. Lozen
James E. McDonald
Myles A. Murray
Jay H. Paul
Richard C. Reed
Johan L. Silfwerbrand
Joe Solomon
Michael M. Sprinkel
Ronald R. Stankie
Joseph E. Tomes
David A. VanOcker
Alexander M. Vaysburd
Kurt Wagner
Patrick M. Watson
Mark V. Ziegler
Consulting Members
Peter Emmons
Noel P. Mailvaganam
Kevin A. Michols
Richard Montani
Don T. Pyle
3.2—Concrete removal, p. 6
3.3—Surface preparation, p. 14
3.4—Quality control and assurance, p. 17
This guide presents recommendations for the selection and application of materials and methods for repairing, protecting, and
strengthening concrete structures. An overview of materials and
methods is presented as a guide for selecting a particular application. References are provided for obtaining in-depth information on
the selected materials or methods.
CHAPTER 4—REPAIR MATERIALS, p. 17
4.1—Introduction, p. 17
4.2—Concrete replacements and overlays, p. 17
4.3—Crack repair materials, p. 27
4.4—Bonding materials, p. 31
4.5—Coatings on reinforcement, p. 32
4.6—Reinforcement, p. 32
4.7—Material selection, p. 33
Keywords: anchorage; coating; concrete repair; joint sealant; placement;
polymer; protective systems; repair materials; structural strengthening.
CONTENTS
CHAPTER 1—INTRODUCTION, p. 2
1.1—Guide use, p. 2
1.2—Repair methodology, p. 2
1.3—Sustainability, p. 6
CHAPTER 5—CONCRETE AND REINFORCEMENT
REPAIR TECHNIQUES, p. 34
5.1—Introduction, p. 34
5.2—Crack repair, p. 34
5.3—Concrete replacement, p. 37
5.5—Anchorage, p. 44
5.6—Quality control and assurance, p. 45
CHAPTER 2—DEFINITIONS, p. 6
CHAPTER 3—CONCRETE REMOVAL AND
SURFACE PREPARATION, p. 6
3.1—Introduction, p. 6
CHAPTER 6—PROTECTIVE SYSTEMS, p. 46
6.1—Introduction and selection factors, p. 46
6.2—Typical problems that can be mitigated with protection systems, p. 46
6.3—Total system concept, p. 47
6.4—Surface treatments, p. 48
ACI Committee Reports, Guides, and Commentaries are
intended for guidance in planning, designing, executing, and
inspecting construction. This document is intended for the use
of individuals who are competent to evaluate the significance
and limitations of its content and recommendations and who
will accept responsibility for the application of the material it
contains. The American Concrete Institute disclaims any and
all responsibility for the stated principles. The Institute shall
not be liable for any loss or damage arising therefrom.
Reference to this document shall not be made in contract
documents. If items found in this document are desired by
the Architect/Engineer to be a part of the contract documents,
they shall be restated in mandatory language for incorporation
by the Architect/Engineer.
ACI 546R-14 supersedes 546R-04 and was adopted and published September 2014
Copyright © 2014, American Concrete Institute
All rights reserved including rights of reproduction and use in any form or by any
means, including the making of copies by any photo process, or by electronic or
mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in
writing is obtained from the copyright proprietors
1
2
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
6.5—Concrete surface preparation and installation
requirements, p. 53
6.6—Joints, p. 54
6.7—Cathodic protection, p. 54
6.8—Chloride extraction, p. 55
6.9—Realkalization, p. 56
CHAPTER 7—STRUCTURAL REPAIR AND
STRENGTHENING, p. 56
7.1—General, p. 56
7.2—Internal structural repair (restoration to original
member strength), p. 56
7.3—External reinforcement (encased and exposed), p. 57
7.4—External post-tensioning, p. 59
7.5—Jackets and collars, p. 60
7.6—Supplemental members, p. 61
Special considerations for repair of structural elements, p.
61
7.7—Repair of concrete columns, p. 61
7.8—Repair of concrete beams, girders, and joists, p. 63
7.9—Repair of concrete structural slabs, p. 64
CHAPTER 8—REFERENCES, p. 65
Authored documents, p. 69
CHAPTER 1—INTRODUCTION
1.1—Guide use
This document provides guidance on removal and preparation, selecting material and application methods for repair,
protection, and strengthening of concrete structures. The
information is applicable to repairing deteriorated or damaged
concrete structures; correcting design or construction deficiencies; and strengthening the structure for new uses or to
comply with current, more restrictive building codes.
Current practices in concrete repair are summarized and
information provided for the initial planning of repair work
and selecting repair materials and methods for various
conditions.
1.2—Repair methodology
The methodology for repairing a concrete structure typically includes a condition assessment of the structure,
designing repairs, developing construction documents,
bidding and negotiation processes, and performing the
repair work. Preparing a maintenance plan for the repaired
structure is also recommended. A basic understanding of
the causes of concrete distress, deterioration, or deficiencies is essential to performing meaningful evaluations and
completing successful repairs (ACI 364.1R). Once the cause
of deterioration or deficiency is determined, the appropriate
repair program can be selected to address these conditions.
Depending on the cause and extent of the damage, repair is
not always warranted.
Assessment of the structure should determine the cause
of the deterioration or deficiency and not focus only on the
symptoms. For example, cracking can be a symptom of
distress that may have a variety of causes, such as restraint
of drying shrinkage, restraint of movement due to thermal
cycling, overloading, corrosion of embedded metal, or inadequate design or construction. The cause of distress should
be assessed for proper selection and implementation of an
appropriate repair program (Fig. 1.2).
1.2.1 Condition assessment—The process of repairing
a concrete structure starts with the evaluation of existing
conditions. The evaluation can be divided into several steps:
a) Reviewing available design and construction documents, previous reports, repair/maintenance records, and test
data, if available;
b) Visually examining the existing structure;
c) Performing structural analysis of members in question
or the structure in its deteriorated condition;
d) Evaluating corrosion activity;
e) Performing invasive or nondestructive testing, or both;
f) Reviewing physical, chemical, and petrographic analysis results of laboratory-tested concrete samples.
Additional information on conducting condition surveys
can be found in ACI 201.1R, 207.3R, 222R, 224.1R, 228.2R,
364.1R, 437R, and 562.
1.2.1.1 Unsafe conditions—During the condition assessment, conditions discovered that pose an immediate safety
issue should be identified and reported to the owner for mitigation. Local building codes may require that the licensed
design professional (LDP) report unsafe conditions to the
authorities and typically require that the owner take measures
to protect the public safety where hazardous conditions
exist. For example, if loose concrete on overhead or vertical
surfaces is discovered, access should be limited in the areas
adjacent to and below until the hazards are removed or stabilized. If structural members exhibit compromised integrity,
these members should be stabilized or the affected areas
removed from service.
1.2.1.2 Global issues—The performance of a structure
depends on maintaining the integrity of the structure and
envelope of the building. If the LDP becomes aware of an
item of concern outside the assigned scope of work that
could compromise the integrity of the structure or jeopardize
public safety, the appropriate parties should be notified for
implementation of remedial action.
1.2.1.3 Determination of cause and extent—During the
condition assessment of a structure, the cause of distress,
deterioration, or deficiency should be determined. Because
many deficiencies are caused by more than one mechanism,
a basic understanding of the causes of concrete deterioration
is essential to determine what has happened to a particular
concrete structure. After completing the assessment, a suitable remedial action plan can be developed, repair applications and materials selected, and contract documents
prepared. If a delay occurs between the condition survey
and performing the repair work, additional deterioration
and distress could occur and consideration should be given
to updating the condition survey to minimize variations
between estimated and actual quantities of repair work.
1.2.2 Design considerations—When designing a concrete
repair, strengthening system, or protective system, the LDP
should consider the safety and serviceability of the structure
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
3
Fig. 1.2—Repair methodology.
during construction and its performance at completion. At a
minimum, the repaired structure should satisfy the building
code requirements for which it was designed. If required by
the governing agency, the repaired structure may have to
satisfy current building code requirements and be repaired
and strengthened to meet these criteria. In any case, it is the
LDP’s responsibility to satisfy applicable code requirements
for all structural components within the LDP’s scope of work.
Structural code provisions such as those contained in ACI
318 may not be directly applicable to the current situation. In
such cases, ACI 562 requirements should be followed. The
LDP should apply basic principles of structural mechanics
and have an understanding of material behavior to evaluate
and design a structural repair, a strengthening procedure,
or a protective system. Several design considerations are
discussed 1.2.2.1 through 1.2.2.6.
1.2.2.1 Current load distribution—In a deteriorated
condition, a structural member or system may distribute
dead and live loads differently than when the structure was
undamaged. Cracking, deteriorated concrete, and corroded
reinforcement can alter the behavior of members, leading
to changes in shear, moment, and axial load distribution.
As concrete and reinforcement are removed and replaced
during the repair operation, these redistributed forces may
be further modified. To understand the final behavior of the
structural system, the engineer should evaluate the redistribution of the forces. To reestablish the original load distribution, a member can be relieved of the load by jacking or
other means before repair implementation. If the structure is
not jacked and the dead load is not relieved, the repaired and
adjacent members may support loads differently than was
assumed in the original design of the structure.
1.2.2.2 Compatibility of materials—If a repair and the
existing substrate materials have the same stiffness or
modulus of elasticity, the behavior of the repaired member
may be assumed to be the same as the original member
before deterioration or damage. Conversely, if the stiffnesses
differ, then the composite nature of the repaired system
should be considered. A mismatch of other material characteristics further exacerbates the effects of thermal change,
vibration, long-term creep, and shrinkage. If the coefficient
of thermal expansion of the repair material differs from that
of the original material, stresses will be generated in both the
repair and original material by temperature changes.
1.2.2.3 Creep and shrinkage—Reduction in length, area,
or volume of both the repair and original materials due to
creep, shrinkage, or both, affect the structure’s serviceability
and durability. As an example, compared with the original
material, high creep or shrinkage of repair materials results
in loss of stiffness of the repair, redistributed forces, and
increased deformations. Controlled-shrinkage cementitious
repair materials and systems can contribute to the reduction
of the volume change effects.
1.2.2.4 Vibration—When the installed repair material is in
a plastic state or until adequate strength has been developed,
vibration of a structure can result in reduced bonding of the
repair material. Isolating the repairs or eliminating the vibration may be a design consideration.
1.2.2.5 Water and vapor migration—Water or vapor
migration through a concrete structure can degrade a repair.
Understanding the cause of the migration and controlling it
should be a repair design consideration.
1.2.2.6 Material behavior characteristics—After a repair
is executed, the structural behavior of the repaired section
American Concrete Institute – Copyrighted © Material – www.concrete.org
4
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
can differ from the behavior of the original section and is
dependent on the characteristics of the repair materials. For
example, if a beam’s steel reinforcement has corroded extensively and has lost part of its tensile load-carrying capacity,
the lost portion of the reinforcement may be replaced by
external strengthening techniques (Chapter 7), such as fiberreinforced polymer (FRP) applied externally to the tension
face of the beam, following repair or replacement of the
deteriorated section caused by steel corrosion. The LDP
should consider the behavior and performance of the new
repair under the expected service and ultimate loads, and
design the repair to provide a level of safety that is at least
equivalent to the original design. Such a design is outside the
scope of ACI 318 and ACI 562 should be used.
1.2.3 Selecting repair methods and materials—Successful
concrete repair depends on the selection and proper application of the materials and methods to be used. ACI 546.3R
provides specific guidelines for the properties of repair
materials and their selection and ACI 546.2R covers underwater repair materials. Repair materials and methods should
be selected with the following considerations.
1.2.3.1 Concrete environment—Repair work can incorporate adjustments or modifications to remedy the cause
of the concrete deterioration, such as reducing exposure
to moisture, changing the water drainage pattern, eliminating sources of erosion and water infiltration, providing
for differential movements, or eliminating exposure to
deleterious substances. However, it is not always possible to
correct causes of deterioration. For example, it may not be
possible to change the environmental exposure of a concrete
structure. In such cases, reasonable efforts should be made
to mitigate the problem by providing appropriate protection
measures.
1.2.3.2 Limiting constraints—Repair work may be
affected by constraints such as limited access to the structure
or areas of repair. For example, underwater concrete deterioration provides access challenges. Other constraints may
include the operating schedule of the structure, weather, and
limitations imposed by the owner of the structure, including
repair budget.
1.2.3.3 Inherent problems—Factors that cannot be
corrected, such as continued exposure to chlorides in deicing
salts, salt water, or deleterious chemicals, should also be
considered. In these cases, repair and protection systems
extend the life of the structure but do not eliminate the
causes of deterioration.
1.2.3.4 Environmental and safety requirements—These
items may have a major impact on the selection of materials, methods, or both. Environmental and occupational
safety constraints are governed by specific requirements and
policies of owners: the Environmental Protection Agency
(EPA); the Occupational, Safety, and Health Administration (OSHA); and local regulations. Refer to International
Concrete Repair Institute (ICRI) 120.1 for information on
further safety aspects relevant to the concrete repair industry.
1.2.3.5 Service life—The intended service life of the
repaired member and structure should be considered in the
selection of repair materials and methods.
1.2.3.6 Constructibility—Availability of repair materials,
equipment and methods, and the technical feasibility of using
them should be evaluated during the material and repair
procedure selection process. Manufacturers or suppliers can
provide assistance in the selection, availability, and cost of
repair materials and for selecting application techniques.
When selecting the appropriate repair material, consider that
the technical data presented in manufacturer’s literature may
be incomplete and insufficient because the tests performed
may not be representative of the use of the material in a
particular application.
1.2.4 Temporary shoring—The repair process, including
concrete removal and reinforcement repair, may alter the
force and load distribution within and between reinforced
concrete members. It is essential that the contractor, in
conjunction with the engineer, determine the need, extent,
and locations of shoring and bracing required as well as
the sequence of repair to satisfy structural safety and force
distribution considerations.
The need for temporary supports, shoring, bracing, and
strengthening to perform the repairs should be determined
before performing repair work. Concrete removal often
exposes reinforcing steel that may have suffered loss of
cross-sectional area; concrete removal around reinforcing
steel reduces the bond between the reinforcement and the
structural element, thereby reducing the shear, bending,
tensile, and compression capacity or stability of the structure. Shoring and bracing may be required to address these
temporary conditions.
If structural analysis is performed, the analysis should
assess the effects of existing conditions and proposed repairs
on the structure, including the evaluation of applicable loads
and dimensional changes resulting from thermal differentials. Areas of special concern that may result in conditions
that require temporary shoring and bracing include redistribution of negative moments in slabs and beams, joint and
connection details, precast spandrel beams and columns, as
well as live loads imposed by repair equipment and material
storage.
In most cases, unless the dead and live loads are relieved
via shoring before the repair work proceeds, the repaired
portion of the element may not be effective in supporting
loads applied after the repair installation is completed. In
cases where restoration of the load-carrying capacity is a
primary concern, existing loads may need to be removed and
members jacked and shored to support dead loads.
1.2.5 Contract documents—The preparation of contract
documents includes drawings, details, and specifications.
Contract documents should include provisions specific to the
project and quality assurance criteria. Because the full extent
of concrete deterioration and distress may not be completely
known until repair work begins, drawings and specifications for repair projects should be prepared with some
flexibility regarding work items such as concrete removal,
surface preparation, reinforcement replacement, and quantities of repair materials. Provisions should be included in the
documents for addressing hidden conditions and potential
changes to the contract estimate of repair quantities.
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Where deterioration is particularly severe or where extensive concrete removal is anticipated, provisions for temporary structural support should be included in the project
documents. Protection of the repair site and adjacent areas
may present unique problems during the execution of a
repair project. Structural components and their supports in
the immediate area of the repairs should be evaluated to
determine if shoring, bracing, or both are required. Redistribution of member internal forces during repair is an important consideration for continuous slabs and beam-and-girder
systems, and is critical for unbonded post-tensioned structures. Repair specifications should be clear and concise,
delineating the scope of work, repair work items, information on existing concrete conditions if available, material
and equipment requirements, surface preparation, installation procedures, quality assurance and testing criteria, and
performance testing standards. Supporting documents referencing specific requirements such as tensile strength, surface
profiling, compressive strength, bond strength, length
change, or shrinkage behavior should be included as appropriate. Details of the concrete repair should be provided,
including parameters for concrete removal and, if possible,
boundaries of concrete removal and replacement along with
any special features of repair system installation necessary,
such as protection systems and strengthening techniques.
Special attention is required for the details of reinforcement
repair or replacement areas and the preparation of existing
concrete before surface protection system application.
1.2.5.1 Contract types—To perform repairs, the contractor
or design/build team typically enters into a contractual
agreement with the owner. This contract defines the scope of
work, price, and schedule. Payment for contractual requirements can be stated in lump sum or fixed-price terms, unit
prices, time and material, or a combination thereof. Refer to
ICRI 130.1R for further information on contract types.
1.2.5.1.1 Lump sum—This contract type is suitable for
a specific, well-defined scope of work in which all repair
items, quantities of work, and work conditions are known.
The contractor is paid a fixed fee for completed work,
regardless of the actual repair items and quantity of work
performed.
1.2.5.1.2 Unit price—This contract type is suitable for a
specific scope of work where all repair items are known but
exact quantities are unknown. The final contract sum for the
repair items covered by unit prices is based on actual quantities of the repair items properly installed by the contractor.
Some individual repair items may be paid on a lump sum or
time and material basis.
1.2.5.1.3 Time and material—This contract type is suitable
for an undefined scope of work where both the repair items
and quantities of work are undefined. The contractor is paid
at a defined hourly rate for labor and reimbursed for materials and equipment with applicable overhead and profit.
1.2.5.2 Performance objectives—Repair documents
should define the structural, environmental, aesthetic, and
protection objectives to be achieved. Mockups are recommended where appropriate; for example, where the color or
5
texture is specified to match the surrounding concrete (ACI
311.1R, 311.4R, and 311.5).
1.2.6 Bid or negotiation process—Selecting a contractor is
one of the most important aspects of a repair project. Contractor
selection can be determined through a bidding process or
negotiated directly with potential contractors. Contractor
selection should be based on demonstrated evidence of expertise and successful previous experience with repairs included
in the project. Manufacturer-approved installers should be
considered for specialized repair products.
1.2.6.1 Prebid conference—Before bids are submitted,
the engineer, owner or owner’s representative, and potential contractors should attend a prebid conference to answer
questions regarding the contract documents and to define
expectations of the owner. This meeting should include a
visit to the repair site.
1.2.6.2 Addenda—Clarifications to the contract documents based on questions raised at the prebid conference,
during the bid period, or both, can be issued in addenda to
the contractors before submission of bids.
1.2.7 Execution of work—Repair work should be executed
in accordance with the contract documents. The concrete
repair process generally consists of removing deteriorated or damaged concrete; surface preparation; repairing,
supplementing, or replacing reinforcing steel; implementing
specified repair techniques; and installing repair materials.
Protecting the executed repairs and strengthening may also
be incorporated into the repair process.
1.2.7.1 Preconstruction conference—Before starting a
project, it is important to have the owner or owner’s representative and LDP attend a meeting with the contractor’s
project manager, superintendent, and foreman to discuss
the parameters, means, methods, and materials necessary to
achieve the repair objectives. At this meeting, the contractor
should present a construction schedule for the owner to
review its acceptability and resolve any conflicts with daily
operations. The frequency and types of required correspondence should be defined among all parties executing
the work to communicate progress, discovered items, and
construction problems.
1.2.7.2 Material submittals and shop drawings—Prior to
use on the project, the contractor should submit technical,
installation, and safety data for proposed repair materials
in accordance with the contract documents to the LDP for
review and acceptance. In addition, shop drawings for items
such as shoring and bracing, reinforcing steel, specific repair
methods, and repair sequencing should also be submitted by
the contractor to the LDP for review and acceptance prior to
initiation of the work.
1.2.7.3 Quality assurance and control—Quality assurance and control measures should be implemented to provide
acceptance criteria, verify conformance to contract documents,
and to verify the properties and quality of the installed repair
materials. ACI 311.4R provides guidance on setup of quality
control, inspection, and testing procedures. ACI 311.1R and
ACI 311.5 provide guidance on inspection and testing.
1.2.7.3.1 Quality assurance—The LDP should outline
quality assurance requirements in the contract documents by
American Concrete Institute – Copyrighted © Material – www.concrete.org
6
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
establishing standards or criteria for acceptance. The quality
assurance program dictates the desired level of quality for
repairs.
1.2.7.3.2 Quality control, inspection, and testing—
Successful completion of the repair program can be verified
by implementing quality control measures during the course
of the work. Such measures include:
a) Periodic site observations by the LDP to verify general
conformance with contract documents;
b) Periodic testing by an independent testing agency to
verify that requirements of the contract documents are met;
c) Contractor supervision of the crew’s work and weather
conditions, including temperature, humidity, and precipitation, which may affect the repair procedure;
d) Recordkeeping by the project team, including documentation of repair locations, repair modifications, quantities installed, documentation reviews by the LDP, weather
conditions, changes to the contract documents, and periodic
progress reports.
1.2.7.3.3 Testing and inspection agency qualifications—
The testing agency should meet the requirements of ASTM
E329. Inspection or testing personnel should be special
inspectors, engineers, the LDP, or ACI-certified, or approved
equal, field/laboratory technicians, as applicable.
1.2.7.4 Project closeout—If requested by the owner and
upon completion of the project, the owner should receive
and retain a project manual from the contractor or LDP
containing copies of relevant contract correspondence issued
during construction. The project manual should include
items such as repair drawings and specifications, additional details or clarifications provided by the engineer, field
and test reports, photographs, submittals, permits, change
orders, requests for information (RFIs) and their responses,
insurance certificates, bonds, pay applications, warranties,
waivers of lien, and as-built drawings.
1.2.8 Maintenance after completion of repairs—Maintenance of the concrete structure and any protection or
strengthening system is recommended after completion of a
concrete repair project. Lack of adequate maintenance may
result in premature failure of the repair or surrounding areas.
If requested by the owner, the LDP should develop a maintenance manual for repair work.
1.2.8.1 Warranty coverage—Warranty requirements
should be followed, including periodic inspections or
recoating of membranes and sealers to ensure that warranty
coverage is maintained. Warranty items should be reviewed
during the warranty period and the contractor contacted to
repair failures that occur under warranty.
1.2.8.2 Periodic inspections—Continued evaluation of the
structure through periodic engineering reviews should be
considered to monitor structural integrity and performance
of repairs.
1.2.8.3 Post-repair monitoring systems—Systems to
detect concrete/system failures should be considered, such
as corrosion monitoring for detecting corrosion and acoustic
monitoring for detecting tendon failures, in post-tensioned
structures.
1.3—Sustainability
A green structure is an environmentally sustainable structure designed, constructed, and maintained to minimize its
impact on the environment (Schokker 2010). The primary
objectives when designing a green structure include reducing
energy consumption, conserving water, and recycling waste.
Repairing and maintaining concrete structures instead of
replacement is a green concept and a sustainable philosophy.
Repairing concrete structures meets sustainability objectives by conserving existing materials and thereby reducing
energy consumption and material waste.
CHAPTER 2—DEFINITIONS
ACI provides a comprehensive list of definitions through
an online resource, “ACI Concrete Terminology,” http://
www.concrete.org/Tools/ConcreteTerminology.aspx. Additional concrete repair definitions are found in the International Concrete Repair Institute (ICRI) terminology database, http://www.icri.org/GENERAL/repairterminology.aspx.
CHAPTER 3—CONCRETE REMOVAL AND
SURFACE PREPARATION
3.1—Introduction
This chapter covers the removal of deteriorated and sound
concrete, and preparation of the concrete surface to receive
new repair materials. Exercising care during the removal and
preparation phases of a repair project can be the most important factor in ensuring the longevity of the repair, regardless of the material or technique used. Concrete should be
removed carefully so as not to damage the existing adjacent
concrete or affect bond of the new repair material.
Care should be taken when removing concrete around
prestressing steel, both bonded and unbonded strands. When
high-energy impact tools such as chipping hammers are
used, operators should avoid contacting the strands with the
tools, as such contact may cause wires to rupture, possibly
leading to strand failure and a reduction in the structure’s
load capacity. Removing surface concrete may also cause
excessive stresses in the concrete to remain and redistribute
secondary forces and moments in indeterminate structures.
The extent of concrete removal should not be permitted to
exceed stress limits in the remaining concrete.
Personal protective equipment should be used in all
processes and the containment, handling, and disposal
of concrete dust, slurry, and debris considered with the
processes employed. Refer to ICRI 120.1 for recommendations on safety in the concrete repair industry to minimize
vibrations and noise.
3.2—Concrete removal
A repair project typically involves removing deteriorated,
damaged, or defective concrete. In most cases, however,
determining the extent of the deteriorated or damaged
concrete requiring removal can be difficult. Common
techniques to identify distressed concrete are sounding by
hammer tapping or by chain drag (ASTM D4580). Deep
delaminations and microcracks may not be detected by
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
hammer sounding or chain dragging. Other techniques
include impact-echo testing (ASTM C1383), ground-penetrating radar (GPR) (ASTM D6087), and infrared thermography (ASTM D4788), typically accompanied by sounding
by hammer tapping, chain drag, or impulse response. Refer
to ACI 228.2R and ICRI 210.4 for additional information
and other test methods used to identify deteriorated and
damaged concrete.
Removing concrete using aggressive methods can damage
concrete that is intended to remain in place. For example,
blasting with explosives or the use of heavy impact equipment can result in additional concrete delamination or
cracking. Impact equipment with a blunt-tipped removal
apparatus can cause more delamination and cracking than
sharp-tipped tools. Removing concrete using impact tools
may also result in microcracking or bruising (Hindo 1990)
to the surface concrete left in place. Unless this damaged
layer is removed, the substrate concrete will be weakened,
possibly resulting in reduced bond strength between the
substrate concrete and repair material. Thus, removing all
damaged or delaminated concrete, including bruising, at the
interface of the repair and the substrate concrete is an important part of achieving a strong bond and composite action
between the substrate concrete and the repair material. If
all deteriorated and damaged concrete is not removed, then
the possibility of repair failure is increased, even if a highquality repair material is used.
In most cases in which concrete has been removed from
a structure by primary means, such as impact methods, the
concrete left in place should be prepared by a secondary
method, such as abrasive blasting or high-pressure water
jetting, to remove any remaining damaged and microcracked
surface material. Careful visual inspection and sounding of
prepared surfaces should be conducted and loose, delaminated, or unsound concrete should be removed before
placing repair materials. The suitability of the substrate to
receive the repair material can be verified by tensile pull-off
testing of trial repairs (ICRI 210.3; ASTM C1583).
Localized removal of deteriorated concrete in a member
includes squaring the edges of the repair area by saw cutting
or chipping square to avoid feather edging the repair material,
removal of delaminated and unsound concrete, and removal
of sound concrete as necessary to provide a minimum thickness of repair material throughout the repair area. Feather
edging of repair materials should be avoided. For shotcrete
repairs, the edges of the removal areas should taper toward
the center of the removal area to avoid acute angles that
can make shotcrete placement more difficult (ACI 506R).
Reentrant corners in the perimeter of removal areas should
be avoided. Large variations in the depth of removal within
short distances should also be avoided, as they may result in
cracking due to varying behavior of the repair materials with
different thicknesses.
Unless otherwise directed by the project specifications,
existing reinforcement should not be cut. Reviewing drawings and using a cover meter or similar device to obtain
data as to the location and depth of existing reinforcement
are good practice. In addition, removing deteriorated and
7
damaged concrete is commonly performed before saw
cutting to determine the location and depth of reinforcement.
3.2.1 General considerations—Concrete repair requires
removal of deteriorated and damaged material. Removing
sound concrete, however, may also be necessary to ensure
that all unsound or contaminated material is removed,
facilitate structural modifications, provide adequate repair
geometry and configuration, and provide development and
encapsulation of reinforcing steel and embedded items. Some
methods may be more effective in sound concrete, whereas
others may work better for deteriorated and damaged concrete.
Concrete removal techniques should be effective, safe
for the structure and the construction workers, economical,
suited to the requirements of the owner, environmentally
friendly, and minimize damage to the concrete left in place.
The removal technique chosen may have a significant effect
on the length of time that a structure will be out of service
for the repair. Some techniques may permit a portion of the
repair work to be accomplished without removing the structure from service. The same removal technique, however,
may not be suitable for all portions of a given structure. In
some instances, a combination of removal techniques may
be more appropriate to speed removal and limit damage
to the existing concrete. Field testing mockups of selected
removal techniques can help determine the best procedures
to use for the repair.
In general, the engineer responsible for the design of
the repair should specify the objectives to be achieved by
the concrete removal, and the repair contractor should be
allowed to select the most effective removal method subject
to the engineer’s acceptance. In some instances, however, the
engineer may need to specify the removal techniques necessary for the repair and those prohibited due to constraints
and logistics of the structure.
The size, quantity, and location of reinforcing steel; size
and type of aggregates; concrete compressive strength
modulus of elasticity as well as the presence of existing coatings, toppings, overlays; and other existing or as-built conditions are important information to consider in determining
the effective method(s) and cost of concrete removal. Whenever possible, this information should be made available to
contractors during bidding. This information is also beneficial to the engineer when they specify concrete removal and
surface preparation criteria and for select repair materials.
3.2.2 Temporary shoring—It is essential to evaluate the
removal operations and their impact on the structure’s integrity throughout the repair process and to limit the extent
of damage to the structure and the existing concrete that
remains. Before removing concrete, the need for temporary supports, shoring, bracing, and strengthening should
be assessed (Fig. 3.2.2a). Structural elements to be repaired
may require temporary shoring, removal of applied loads, or
both, to prevent damaging structural deformations, buckling
or movement of reinforcement, or possible collapse. A structural analysis may need to be performed to assess the effects
of existing conditions and proposed repairs on the structural
integrity of the building and the need for temporary shoring.
American Concrete Institute – Copyrighted © Material – www.concrete.org
8
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 3.2.2a—Temporary shoring parking garage floor (left) and balcony slabs (right).
Care should be used during removal of concrete to avoid
cutting and damaging existing reinforcing steel (Fig. 3.2.2b).
Because embedded reinforcement may not be located in the
specified position and is not visible before concrete removal,
unanticipated damage can occur when saw cutting and
removing concrete. This damage, as well as excess concrete
removal, could affect structural integrity during repairs and
the need for temporary shoring.
3.2.3 Quantity of concrete to be removed—In most repair
projects, all damaged or deteriorated concrete should be
removed because deterioration continues with time. The
anticipated quantity of concrete removal is directly related
to the extent of the distress, repair or removal technique, and
elapsed time between the initial survey and repair construction; potential quantity overruns may be realized between
preparation of the quantity estimates and actual removal.
Estimating inaccuracies can be minimized by a thorough
condition survey performed as close as practical to the time
the repair work is executed. When, by necessity, the condition survey is performed far in advance of the repair work,
estimated removal quantities should be increased to account
for continued deterioration. Because most concrete repair
projects are based on unit prices, repair areas should be
accurately measured upon completion of the work. This is
typically done jointly by the engineer and the contractor. It
is not uncommon for final measured quantities to exceed the
initial estimated quantities. Refer to ICRI 130.1R for guidelines for methods of measurement for concrete repair work.
3.2.3.1 Anodic ring (halo) effect—Accelerated corrosion
occurs where reinforcement located in existing contaminated concrete extends into repair area containing uncontaminated repair material due to the difference in electrical
potential between the contaminated and uncontaminated
concrete volumes (6.2.5). In general, concrete removal
should continue until no further delamination, cracking, or
significant corrosion is observed along the reinforcing steel.
Additional measures should be considered to minimize
future concrete damage due to corrosion if chloride contamination or carbonated concrete will remain beyond the repair
area. Concrete excavation that damages the bond of the
reinforcing steel to the existing concrete requires additional
concrete removal and undercutting of the reinforcing steel.
Fig. 3.2.2b—Saw cutting perimeter of repair area.
3.2.3.2 Removal of concrete surrounding reinforcing
steel—Concrete removal should include the removal of deteriorated and damaged concrete surrounding existing reinforcing steel. Care should be used to prevent further damage
to the reinforcing or prestressing steel caused by the process
of removing the concrete. For this reason, a cover meter or
reinforcing bar locator, along with structural drawings if
available, should be used to help determine the depth, size,
quantity, and approximate location of the existing reinforcement within the repair area.
Once the selected concrete has been removed within the
repair area, a less invasive removal method, such as light
(15 lb [67 N]) chipping hammers should be used to remove
the concrete around exposed reinforcement. Care should be
taken to not damage the reinforcement or otherwise cause
loss of reinforcing bond to the existing remaining concrete.
If the existing reinforcing steel is only partially exposed after
concrete removal, it may not be necessary to remove additional concrete to expose the full circumference of the reinforcement, provided the reinforcement is uncorroded, has
not lost bond to the existing concrete; the existing concrete
is sound and not chloride-contaminated (AASHTO T 260,
ASTM C1152, and ASTM C1218); and the pH (ASTM
F710) has not been affected by carbonation (6.2.4) or acid
attack. When the exposed reinforcing steel has loose rust,
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
corrosion products, is not well bonded to the surrounding
concrete, or if the concrete surrounding the reinforcing steel
is chloride-contaminated, concrete removal should continue
around the reinforcing steel to create a minimum of 0.75 in.
(19 mm) clearance to the surrounding concrete or 0.25 in. (6
mm) larger than the coarsest aggregate in the repair material.
Undercutting the exposed reinforcing steel provides clearance around the reinforcing steel for cleaning, complete
bonding of the repair material to the existing concrete, and
structurally secures the repair (ICRI 310.1R). Pay special
attention when removing concrete around both bonded
and unbonded prestressed steel strands. Excessive concrete
removal can lead to changes in strand profile, reduce forces
in the strand, and compromise the integrity of the structure.
3.2.3.3 Preparation of repair perimeter—Following the
removal of unsound concrete, the perimeter of the repair
area should be saw cut to create a simple symmetrical
configuration, preferably square or rectangular with square
corners. Saw cut to a depth of 0.50 to 0.75 in. (13 to 19
mm) at the repair perimeter to provide a vertical edge for
consolidating the repair material. Saw cutting to a lesser
depth may be necessary at locations where the reinforcing
steel has reduced concrete cover. A perimeter saw cut is
often unnecessary with concrete removal methods such as
high-pressure water jets. Refer to the manufacturer’s recommendations for the selected repair material. Following saw
cutting, some removal of sound concrete may be required to
achieve the repair perimeter. Care should be taken to avoid
abrupt changes in depth withi n the repair area, as the repair
material is more susceptible to cracking at these locations.
3.2.4 Concrete removal methods—Removal and excavation methods can be categorized by the way in which the
process acts on the concrete. Common processes are cutting,
impacting, and high-pressure water jets (hydrodemolition).
Other less-common methods of concrete removal are also
available, including blasting and presplitting methods, but
are typically only used for large-scale concrete removal.
Table 3.2.4 provides a general description of these processes,
lists the specific removal techniques within each category,
and provides a summary of information on each technique.
Refer to ICRI 310.1R, 310.2R and Society for Protective
Coating (SSPC)-SP13/NACE 6 for additional information
on concrete removal.
3.2.4.1 Cutting methods—Cutting methods generally
employ mechanical sawing or high-pressure water jets to
cut around the perimeter of concrete sections to permit their
removal. The size of the sections cut free is governed by the
available lifting and transporting equipment. The cutting
methods include high-pressure water jets, saw cutting,
diamond wire cutting, mechanical shearing, and stitch drilling.
3.2.4.1.1 High-pressure water jet without abrasives—A
narrow high-pressure water jet driven at high velocities,
commonly producing pressures of 10,000 to 40,000 psi
(69 to 276 MPa) to cut and remove concrete and prepare
concrete surfaces. Section 3.2.4.3 describes using a water
jet as a concrete removal method. High-pressure water jets
without abrasives will remove concrete but will not cut or
damage the reinforcing steel. The addition of abrasives to
9
the water jet can result in cutting of the concrete and the
reinforcing steel.
3.2.4.1.2 Saw cutting—Diamond or carbide saws are
available in sizes ranging from small and capable of being
hand-held, to large and capable of cutting depths of approximately 5 ft (1.5 m) to substantially larger depths.
3.2.4.1.3 Diamond wire cutting—Diamond wire cutting is
accomplished with a wire containing nodules (small lumps)
impregnated with diamonds. The wire is wrapped around the
concrete mass to be cut and connected with a power pack to
form a continuous loop. The loop is spun in the plane of the
cut while being drawn through the concrete member. This
system can be used to cut a structure of any size as long as
the wire can be wrapped around the concrete. The limits of
the power source determine the size of the concrete structure
that can be cut. This system provides an efficient method for
cutting and dismantling large or small concrete structures.
3.2.4.1.4 Mechanical shearing—The mechanical shearing
method uses hydraulically powered jaws to cut or crush
concrete and shear the reinforcing steel. This method is
applicable for making cutouts through slabs, decks, and other
thin concrete members and especially applicable where total
demolition of the member is desired. The major limitation of
this method is that cuts need to start from free edges or from
holes made by hand-held breakers or other means.
3.2.4.1.5 Stitch drilling—The stitch drilling method uses
overlapping boreholes along the removal perimeter to cut
out sections. This method is applicable for making cutouts in
concrete members where access to only one face is possible,
and the depth of cut is greater than can be economically cut
by the saw cutting and diamond wire cutting methods. The
primary drawback of stitch drilling is the potential for costly
removal complications if the cutting depth exceeds the
accuracy of the drilling equipment, so that uncut concrete
remains between adjacent holes.
3.2.4.2 Impact methods—Impact methods are the most
commonly used concrete removal techniques. Impact
methods involve striking a concrete surface repeatedly with
a high-energy tool with hardened points or large mass to
fracture and spall the concrete. Using impact methods for
concrete removal can result in microcracking of the surface
concrete left in place and creating a weakened plane below
the bond line of the repair material. Impact methods also
transmit vibrations through the structure and reinforcing
steel, which may cause further damage and loss of bond
between the reinforcing steel and existing concrete. Factors
such as the weight, size, and power of the impact removal
equipment should be considered, balancing the desire for
productive removal while minimizing damage and microcracking. Secondary methods, such as abrasive blasting
and water blasting, should be considered to remove microcracking following the use of impact methods. Tensile pulloff testing in accordance with ICRI 210.3 or ASTM C1583
is recommended to determine the suitability of the final
prepared surface to receive repair materials and coatings.
3.2.4.2.1 Hand-held breakers—The hand-held breaker or
chipping hammer is probably the most common and best
known of all concrete removal devices. Hand-held breakers
American Concrete Institute – Copyrighted © Material – www.concrete.org
10
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Table 3.2.4—Summary of features, considerations, and limitations for concrete removal methods
Category
Features
Water-jet cutting
a) High-pressure water jet without abrasives
(uses perimeter cuts to remove large b) Applicable for making cutouts through slabs,
pieces of concrete)
decks, and other thin concrete members
c) Cuts irregular and curved shapes
d) Makes cutouts without overcutting corners
e) Cuts flush with intersecting surfaces
f) No heat, vibration, or dust is produced
g) Handling of debris is efficient because bulk of
concrete is removed in large pieces
Saw cutting (applicable for making a) Makes precision cuts
cutouts through slabs, decks, and
b) No vibration is produced
other thin concrete members)
c) Handling of debris is efficient because bulk of
concrete is removed in large pieces
Diamond wire cutting (applicable
for cutting large, thick pieces of
concrete)
a) The diamond wire chain can be any length
b) No dust or vibration is produced
c) Large blocks of concrete can be lifted out by a
crane or other mechanical methods
d) The cutting operation can be efficient in any
direction
Mechanical shearing
(applicable for making cutouts
through slabs, decks, and other thin
concrete members)
a) Steel reinforcement can be cut
b) Limited noise and vibration are produced
c) Handling of debris is efficient because bulk of
concrete is removed in large pieces
Stitch drilling
(applicable for making cutouts
through concrete members where
access to only one face is feasible)
a) Handling of debris is more efficient because
bulk of concrete is removed in large pieces
Impacting (uses repeated striking of
the surface with a mass to fracture
and spall the concrete)
a) Hand-held breakers
b) Applicable for limited volumes of concrete
removal
c) Applicable where blow energy must be limited
d) Widely available commercially
e) Can be used in areas of limited work space
f) Produces relatively small and easily handled
debris
a) Can be used for vertical and overhead surfaces
b) Widely available commercially
c) Produces easily handled debris
Boom-mounted breakers (applicable for full-depth removal of
slabs, decks, and other thin concrete
members and for surface removal
from more massive concrete
structures)
Considerations/limitations
a) Cutouts for removal limited to thin sections
b) Cutting is typically slower and more costly than diamond
blade sawing
c) Moderate levels of noise may be produced
d) Controlling flow of waste water may be required
e) Additional safety precautions are required due to the high
water pressure produced by the system
f) Does not cut reinforcing steel
a) Cutouts for removal limited to thin sections
b) Performance is affected by type of diamonds and the
diamond-to-metal bond in blade segments (segment selection is
based on aggregate hardness)
c) The higher the percentage of steel reinforcement in cuts, the
slower and more costly the cutting
d) The harder the aggregate, the slower and more costly the
cutting
e) Controlling flow of waste water may be required
a) The cutting chain must be continuous
b) Access to drill holes through the concrete must be available
or access around the full section of the structure if the full
section is to be cut
c) Water must be available to the chain
d) Controlling the flow of waste water may be required
e) The harder the aggregate or concrete, and the higher the
percentage of steel, the slower and more costly the cutting
f) Performance is affected by the quality, type, and number of
diamonds as well as the diamond-to-metal bond in the chain.
a) Limited to thin sections where an edge is available or a hole
can be made to start the cut
b) Exposed reinforcing steel is damaged beyond reuse
c) Remaining concrete is damaged
d) Extremely rugged profile is produced at the cut edge
e) Ragged feather edges remain after removal
a) Rotary-percussion drilling is more expedient and economical
than diamond core drilling; however, it may result in more
damage to the concrete that remains, especially at the point of
exit from the concrete
b) Depth of cuts is dependent on accuracy of drilling equipment in maintaining overlap between holes with depth and
diameter of the boreholes drilled. The deeper the cut, the
greater borehole diameter required to maintain overlap between
adjacent holes and the greater the cost
c) Uncut portions between adjacent boreholes will hamper or
prevent the removal
d) Cutting reinforced concrete increases the cutting time and
increases the cost. Aggregate toughness for percussion drilling
and aggregate hardness for diamond coring will affect cutting
cost and rate.
e) Personnel must wear hearing protection due to high noise
levels.
a) Performance is a function of concrete soundness and aggregate toughness
b) Significant loss of productivity occurs when breaking action
is other than downward
c) Removal boundaries will likely require saw cutting to avoid
feathered edges
d) Concrete that remains may be damaged (microcracking)
e) Produces high levels of noise, dust, and vibration
a) Blow energy delivered to the concrete may have to
be limited to protect the structure being repaired and the
surrounding structures from damage
b) Performance is a function of concrete soundness and aggregate toughness
c) Damages remaining concrete
d) Damages reinforcing steel
e) Produces feathered edges
f) Produces high level of noise and dust
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
11
Table 3.2.4 (cont.)—Summary of features, considerations, and limitations for concrete removal methods
Category
Scabblers
Features
a) Low initial cost
b) Can be operated by unskilled labor
c) Can be used in areas of limited work space
d) Removes deteriorated concrete from wall or
floor surfaces efficiently
e) Readily available commercially
Needle scaler
a) Can be used in areas of limited work space
(applicable for limited volumes of b) Can be used for vertical and overhead surfaces
concrete removal)
c) Produces relatively small and easily handled
debris
Scarifier/milling (applicable for
a) Boom-mounted cutters are applicable for
removing deteriorated concrete
removal from wall and ceiling surfaces
surfaces from slabs, decks, and mass b) Removal profile can be controlled
concrete)
c) Method produces relatively small and easily
handled debris
Erosion/expansive pressure
a) Does not damage the concrete that remains
(hydrodemolition)
b) Steel reinforcement is left clean and undam(applicable for removal of deteaged for reuse
riorated concrete from surfaces of c) Method produces easily handled aggregatebridges and parking decks and other sized debris
deteriorated surfaces where removal
depth is 6 in. [150 mm] or less)
Considerations/limitations
a) High cyclic energy applied to a structure will produce fractures in the surface of the remaining concrete
b) Produces high level of noise and dust
c) Limited depth removal
a) Limited concrete removal depth
b) Concrete that remains can be damaged (microcracking)
c) Produces feathered edges
a) Removal is limited to concrete without steel reinforcement
b) Sound concrete reduces the rate of removal
c) Can damage concrete that remains (microcracking)
d) Noise, vibration, and dust are produced
a) Productivity is reduced when sound concrete is being removed
b) Removal profile will vary with changes in depth of
deterioration
c) Method requires large source of potable water to meet water
demand
d) Waste water may have to be controlled
e) A permit may be required if waste water is to enter a waterway
f) Personnel must wear hearing protection due to the high level
of noise produced
g) Flying debris is produced
h) Additional safety requirements are required due to the high
pressures produced by these systems
Blasting—explosives
a) Most expedient method for removing large
a) Requires highly skilled personnel for design and execution
(uses rapidly expanding gas confined volumes where concrete section is 10 in. (250
b) Stringent safety regulations must be complied with
within a series of boreholes to
mm) thick or more
regarding the transportation, storage, and use of explosives due
produce controlled fracture and
b) Produces good fragmentation of concrete debris to their inherent dangers
removal of concrete)
for easy removal
c) Blast energy must be controlled to avoid damage to
surrounding structures resulting from air-blast pressure, ground
vibration, and flying debris
Presplitting
a) Large sections can be presplit for removal,
a) Development of presplitting plane is decreased by presence
(uses hydraulic jacks, water pulses, thereby making handling of debris more efficient of reinforcing steel normal to presplitting plane
or expansive agents in a pattern of b) Development of presplitting plane in direction b) Presplit opening must be wide enough to allow cutting of
boreholes to presplit and fracture the of boreholes depth is limited
steel reinforcement
concrete to facilitate removal)
c) Development of presplitting plane is decreased c) Secondary means of breakage may be required to complete
by presence of reinforcing steel normal to
removal
presplitting plane
d) Loss of control of presplitting plane can result if boreholes
d) Presplit opening must be wide enough to allow are too far apart or if holes are located in severely deteriorated
cutting of steel reinforcement
concrete
e) Secondary means of breakage may be required
to complete removal
a) Loss of control of presplitting plane can result
if boreholes are too far apart or if holes are located
in severely deteriorated concrete
Hydraulic splitter
a) Typically less costly than cutting members
(applicable for presplitting slabs,
b) Direction of presplitting can be controlled by
decks, walls, and other thin to
orientation of wedges and drill hole layout
medium concrete members)
c) Can be used in areas of limited access
d) Limited skills required by operator
e) No vibration, noise, or fly rock is produced
except by the drilling of boreholes and secondary
breakage method
Water pulse splitter
a) Economical, portable, rugged, and easy to use
a) Requires boreholes at close intervals to control crack
and maintain
propagation
b) Devices have self-contained power sources
b) Control of crack plane depth is limited
c) Negligible vibration
c) Not applicable to vertical surfaces
d) Produces some noise
e) Drill holes must hold water
Expansive agents (applicable where a) Can be used to produce vertical splitting planes a) Best used in gravity-filled vertical or near-vertical holes
9 in. [230 mm] or more of a concrete of significant depth
b) Agents of putty consistency are available for use in horiface is to be removed)
b) No vibration, noise, or flying debris is produced zontal or overhead holes
other than that produced by the drilling of borec) Development of presplitting plane is decreased by presence
holes and secondary breakage method
of reinforcing steel normal to presplitting plane
American Concrete Institute – Copyrighted © Material – www.concrete.org
12
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 3.2.4.2.1—Hand-held breakers.
Fig. 3.2.4.2.2—Boom-mounted breaker.
are available in various sizes with different levels of energy
and efficiency (Fig. 3.2.4.2.1). These tools are generally
defined by weight and vary in size from 8 to 90 lb (3.5 to
41 kg). Note that the larger the hammer, the greater the
potential for microcracking. Smaller hand-held breakers
are commonly used in partial depth removal of sound and
unsound concrete and concrete removal around reinforcing
steel because they minimize damage to the existing concrete
and reinforcing steel. Larger breakers are used for removal
of large volumes of concrete. Exercise care when selecting
the size of breakers to minimize damage to the structure
and to avoid shattering or breaking through the remaining
section. Sharp-pointed tools also tend to reduce the potential for microcracking of the surface concrete left in place,
as do lightweight breakers used at a shallower angle to the
removal substrate.
3.2.4.2.2 Boom-mounted breakers—The boom-mounted
breaker is similar to the hand-held breaker except that it is
mechanically operated and considerably larger than a handheld breaker (Fig. 3.2.4.2.2). Boom-mounted breakers differ
from hand-held breakers as they function on the principle
of high energy and low frequency rather than low energy
and high frequency, and are driven by compressed air or
hydraulic pressure. The reach of the hydraulic arm enables
the breaker to be used on vertical or overhead surfaces at a
considerable distance above and below the machine level.
The boom-mounted breaker is a highly productive means of
removing concrete; however, the high-cycle impact energy
delivered to a structure by the breaker generates forces that
may damage the existing concrete and reinforcing steel and
adversely affect the integrity of the structure.
3.2.4.2.3 Scabblers—Scabblers are best known for their
ability to remove shallow depths of concrete from a surface.
Scabblers impact the concrete with cutting heads to create a
chipping and pulverizing action. Scabbler heads are available in various sizes and geometrical shapes, and varying
numbers of heads may be mounted on the cylinders. Equipment size depends on the number of cylinders. The equipment is normally driven by compressed air. A scabbler is
designed to remove deteriorated or sound concrete from
horizontal, vertical, and overhead surfaces to relatively
shallow depths (1/8 to 3/4 in. [3 to 19 mm]). Scabblers
produce a very irregular surface with a fractured coarse
aggregate profile and typically cause microcracking of the
concrete surface. Scabblers can also remove brittle coatings
and provide deep profiling in preparation for overlays and
other repair materials.
3.2.4.2.4 Needle scaler—Needle scaling uses the pointed
tips of a bundle of steel rods contained by a steel tube to
impact and remove concrete to shallow depths (1/16 to
1/8 in. [1.5 to 3 mm]) at horizontal, vertical, and overhead
surfaces. This method is typically used at edges and areas
inaccessible by larger equipment. Needle scaling creates the
potential for microcracking of the concrete surface. Needle
scalers are also used for removing existing coatings and
preparation of surfaces for coatings and thin overlays.
3.2.4.2.5 Scarifier—A scarifier is a concrete removal
device that uses rotary action and several cutter bits mounted
on a drum to fracture and pulverize the concrete from a
surface. Concrete removal depths typically range from 1/8
to 3/4 in. (3 to 19 mm) and may require multiple passes
with the equipment. Scarifying can remove deteriorated
and sound concrete in which some of the concrete contains
form ties and wire mesh. Scarifiers are available in a range
of sizes for removing deteriorated concrete on horizontal,
vertical, and overhead surfaces. Advantages include welldefined limits of concrete removal, relatively small and
easily handled concrete debris, and simplicity of operation.
Scarifiers may cause microcracking in the concrete. Scarifiers are also used for the removal of brittle coatings and
adhesives, and profiling of concrete surfaces in preparation
for high-build coatings, overlays, and other repair materials.
3.2.4.2.6 Milling methods—Milling methods can remove
a specified amount of concrete from large areas of horizontal
or vertical surfaces. The removal depth typically ranges
from 1/4 to 4 in. (6 to 100 mm). Removal depth is determined by the number and size of teeth. Milling operations
typically leave a sound surface with fewer microfractures
than impact methods (Virginia Transportation Research
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Council 2001). Tensile pull-off testing is recommended on
surfaces prepared by milling to determine the suitability of
the surface to receive repair materials.
3.2.4.3 Hydrodemolition—High-pressure water jetting
(hydrodemolition) can be used to remove sound and
unsound concrete on horizontal, vertical, and overhead
surfaces without damaging the existing reinforcing steel and
without causing microcracking of the remaining in-place
concrete. Hydrodemolition disintegrates concrete and
leaves a saturated, rough, irregular surface profile capable
of providing an excellent composite bond with the repair
material (Fig. 3.2.4.3). The method is very efficient at
removing unsound concrete over large areas of the concrete
surface cleaning the reinforcing steel in the process by
abrasive action of the water and the pulverized concrete.
The existing concrete surface is ready for placement of the
repair material, provided the surface is thoroughly cleaned
and rinsed following hydrodemolition and any ponded water
is removed. Hydrodemolition uses high-pressure pumps
capable of generating pressures from 10,000 to 40,000 psi
(69 to 276 MPa) with water flow rates between 6 to 100
gpm (25 and 380 lpm) (ICRI 310.3). The high-pressure
water jet may be applied using a robotic removal unit. The
robotic unit moves the water jet uniformly over the concrete
to be removed. Hydrodemolition can also remove deteriorated concrete that exists below the specified removal depth.
This is called selective removal and it is used to help ensure
that all unsound concrete has been removed. The water jet
does not transmit vibration into the concrete and will not
cause further damage to the existing structure. Hydrodemolition is a wet process that minimizes dust from the work
area and uses large quantities of water that must be collected
and disposed of properly. Wastewater contains suspended
particles and typically has a pH of 11 to 12.5. The wastewater must be filtered and treated to reduce the particulates
and the alkalinity reduced to a pH typically between 5 and
10 before discharge. Hydrodemolition should not be used
in post-tensioned structures with unbonded tendons, except
under the direct supervision of a structural engineer.
Water jet hand lances operating at pressures of 10,000
to 40,000 psi (69 to 276 MPa) with water flows of 2 to
12 gpm (8 to 45 lpm) are available to remove concrete in
areas difficult to access with larger equipment (ICRI 310.3;
SHRP-S-336).
Hydrodemolition is also used to remove coatings and
waterproofing membrane systems. This removal is generally accomplished with a multiple-jet nozzle instead of the
single-jet nozzle (ICRI 310.3; ACI RAP-14). Hydrodemolition is also used in surface preparation for overlays.
Typically, this method is not used for small-scale repairs
primarily for reasons of practicality, containment, and equipment mobilization. Additionally, large volumes of water are
required for this method as well as the subsequent water
treatment and disposal.
3.2.4.4 Blasting methods—Blasting methods generally use
rapidly expanding gas confined within a series of bore holes
to produce controlled fractures and removal of the concrete.
13
Fig. 3.2.4.3—Hydrodemolition.
The only blasting method addressed in this report is explosive blasting.
Explosive blasting is the most cost-effective and expedient means for removing large quantities of concrete. An
example is portions of large mass concrete foundations or
walls. This method involves drilling bore holes, placing
an explosive in each hole, and detonating the explosive.
Controlled-blasting techniques minimize damage to the
material that remains after blasting. One such technique
(cushion blasting) involves drilling a line of 3 in. (75 mm)
diameter or smaller bore holes parallel to the removal face,
loading each hole with light charges of explosive (typically a
detonating cord) distributed along its length, cushioning the
charges by stemming each hole completely or in the collar
with wet sand, and detonating the explosive with electric
blasting caps. The uniform distribution and cushioning of
the light charges produce a relatively sound surface with
little overbreak.
Blasting machines and electrical blasting-cap delay series
are also used for controlled demolition and use proper
timing sequences to provide greater control in reducing
ground vibration. Controlled blasting has been used successfully on numerous repair projects. Selecting the proper
charge weight, borehole diameter, and borehole spacing for
a repair project depends on the location of the structure, the
acceptable degree of vibration and damage, and the quantity
and quality of concrete to be removed. If at all possible, a
pilot test program should be implemented to determine the
optimum parameters. Because of the inherent dangers in the
handling and usage of explosives, all phases of the blasting
project should be performed by qualified licensed personnel
with proven experience and ability.
3.2.4.5 Presplitting methods—Presplitting methods use
hydraulic splitters, water pressure pulses, or expansive
chemicals used in bore holes drilled at points along a predetermined line to induce a crack plane for the removal of
concrete. The pattern, spacing, and depth of the bore holes
affect the direction and extent of the crack planes that propagate. Presplitting is generally used in mass concrete structures or unreinforced concrete.
American Concrete Institute – Copyrighted © Material – www.concrete.org
14
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
3.2.4.5.1 Hydraulic splitter—A hydraulic splitter is a
wedging device used in predrilled bore holes to split concrete
into sections. This method has potential as a primary means
for removal of large volumes of material from mass concrete
structures. Secondary means of separating and handling the
concrete, however, may be required where reinforcing steel
is involved.
3.2.4.5.2 Water-pulse splitter—The water-pressure pulse
method requires that the boreholes be filled with water. A
device, or devices, containing a very small explosive charge
is placed into one or more holes, and the explosive is detonated. The explosion creates a high-pressure pulse that is
transmitted through the water to the structure, cracking the
concrete. Secondary means may be required to complete the
removal of reinforced concrete. This method does not work
if the concrete is so badly cracked or deteriorated that it does
not hold water in the drill holes.
3.2.4.5.3 Expansive product agents—Commercially available cementitious expansive products, when correctly mixed
with water, exhibit a large increase in volume over a short
period of time. By placing the expansive agent in boreholes
located in a predetermined pattern within a concrete structure, the concrete can be split in a controlled manner for
removal. This technique has potential as a primary means of
removing large volumes of material from concrete structures
and is best suited for use in holes of depth greater than 12 in.
(300 mm). Secondary means may be required to complete
the separation and removal of concrete from the reinforcement. A key advantage to the use of expansive agents is the
relatively nonviolent nature of the process and the reduced
tendency to disturb the adjacent concrete.
3.3—Surface preparation
Following concrete removal, the most important step
in the repair of a concrete structure is the surface preparation and cleanliness of the repair area. Regardless of the
nature, sophistication, or cost of the repair material, the
repair is only as good as the surface preparation. To ensure
the desired behavior in the structure, repairs to reinforced
concrete should also include proper preparation of the reinforcing steel and concrete surface to develop a good bond
with the repair material. This section discusses the surface
preparation of concrete and reinforcing steel for a repair.
Project documents should include requirements for inspection of substrates to confirm adequate completion of preparation measures prior to placement of the repair materials.
3.3.1 General considerations—Surface preparation
consists of the final steps necessary to prepare the concrete
surface to receive repair materials. The appropriate preparation of the concrete surface depends on the procedures
used to remove the concrete and on the type of repair to be
undertaken.
Most of the concrete removal methods described in 3.2 can
also be used for surface preparation. An effective method for
concrete removal, however, may not be effective or appropriate for a specific surface preparation requirement. For
example, some concrete removal methods leave the concrete
surface too rough or irregular for the intended repair material
Fig. 3.3.1—Concrete surface profile.
such as membrane coatings. In these cases, removal methods
specifically intended for the final surface preparation may be
required. ICRI 310.2R provides a concrete surface profile
(CSP) system for determining the surface profile necessary for various repair applications (Fig. 3.3.1). Sandpaper
grit size is also commonly used as a means to characterize
surface profile (ASTM D7682).
Some concrete removal methods damage or weaken the
remaining concrete surface. This may be critical if structural
bonding of the repair material is important. For example,
microcracking of the concrete surface occurs when using
certain removal methods. Left in place, microcracking
often produces a weakened plane in the underlying concrete
substrate, below the bond line. In this case, a less invasive
and aggressive method of final surface preparation, such as
abrasive or water blasting, may be necessary to remove the
damaged surface layer.
In many repair situations, the proposed repair requires
only surface profiling, exposure of coarse or fine aggregate,
removal of a thin layer of damaged concrete, or cleaning
of the concrete surface. Within the limits described in
the previous paragraph, several of the concrete removal
methods described in 3.2 can be used for this type of surface
preparation. The referenced methods offer a wide range of
surface characteristics and results. For example, the required
surface preparation may vary from a light abrasive cleaning
suitable for the application of a coating, to a deeper roughening and surface profiling necessary for good bond and reliable performance of the repair material. Selecting a suitable
method of surface preparation is extremely important, as it
influences the cost and performance of the repair.
3.3.2 Surface preparation methods—Common surface
preparation techniques include abrasive blasting, shotblasting, waterblasting, and cleaning methods. Table 3.3.2
provides a general description of surface preparation techniques. Refer to ICRI 310.2R for additional information on
these methods.
3.3.2.1 Abrasive blasting—Abrasive blasting removes
and cleans concrete by propelling an abrasive medium in
compressed air or high-pressure water at high velocity
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
15
Table 3.3.2—Summary of features and considerations/limitations for surface preparation methods
Category
Abrasive blasting— Sandblasting
(dry/wet)
(uses equipment that propels an abrasive medium at high velocity at the
concrete to abrade the surface)
Low-pressure water blasting (with
abrasives)
Abrasive blasting—Shotblasting
Chemical cleaning
Acid etching
Low-pressure water cleaning
(without abrasives)
Features
Considerations/limitations
a) Efficient method for roughening the surface and a) Dry sandblasting procedure produces large volumes of dust
exposing aggregate
b) Wet sandblasting is slow
b) Cleans reinforcing steel
c) Removes surface contamination
a) Selectively removes defective concrete
b) Precise control of removal process
c) Cleans reinforcing steel while removing
concrete
d) Produces minimal damage to remaining
concrete
e) Produces no heat or dust
f) Abrasives enable jet to cut steel reinforcement
and hard aggregates
a) Efficient method for roughening the surface and
exposing aggregate
b) Low dust emissions
c) Removes surface contaminants
d) Controlled depth of concrete removal
e) Readily available commercially
a) Application of chemicals to remove dirt and
contaminants from surface
b) Additional surface preparation may be necessary to remove cleaning chemical residue
c) Follow cleaning chemical manufacturer’s
recommendations
d) Follow coating manufacturer’s instructions
a) Effective in removing cement-based materials
b) Increases porosity of concrete surface
a) Effectively removes surface contaminants
without chemical residue
b) Minimal protection of adjacent areas necessary
against the concrete surface to abrade and pulverize it. Abrasive blasting is commonly used to clean reinforcing steel and
clean and profile concrete surfaces in preparation for sealers,
coatings, and overlays. The method can also remove surface
contaminants, brittle coatings, and adhesive films. The
method can be used on horizontal, vertical, and overhead
surfaces. Depth of concrete removal depends on the duration of the blasting as well as the size and cutting efficiency
of the abrasive medium. Commonly used methods include
sandblasting, shotblasting, and high-pressure water blasting.
3.3.2.1.1 Sandblasting—Sandblasting is the most
commonly used abrasive blasting method in the construction
industry (Fig. 3.3.2.1.1). The process uses common sands,
silica sands, metallic sands, granular slags, or other media
for the abrasive medium. The process may be executed by
three techniques (3.3.2.1.1.1 through 3.3.2.1.1.3).
3.3.2.1.1.1 Dry sandblasting—In dry sandblasting, abrasive particles are propelled at concrete and steel surfaces in
a stream of compressed air at a minimum pressure of 100 psi
(0.7 MPa). The compressor size will vary depending on the
size of the sandblasting pot. The abrasive particles are typically angular and may range in size from passing a No. 70
to a No. 4 (212 to 4.75 mm) sieve. The rougher the required
surface condition, the larger the abrasive particle size
necessary. Finer sands are used for removing contaminants
a) High initial investment
b) Additional protection and safety procedures may be required
due to water pressure
c) Controlling flow of contaminated waste water may be
required
a) Large units may produce high noise levels
b) High voltage power requirements
a) Additional surface preparation may be necessary
b) May not be effective in removing all contaminants
c) May have strong chemical odor
d) Protection of adjacent area necessary
a) Protective clothing is necessary
b) Large amounts of water necessary
c) May permanently stain concrete
d) Protection of adjacent area necessary
e) May contaminate and damage remaining concrete surface
a) Control of large amounts of water
b) Removal of small amounts of concrete may be noticeable
Fig. 3.3.2.1.1—Sandblasting.
and laitance from the concrete and loose scale from reinforcing steel. Coarser sands are commonly used to expose
fine and coarse aggregates in the concrete by removing
the paste or tightly bonded corrosion products from reinforcing steel. Although abrasive blasting has the ability to
remove concrete, it is not economically practical to remove
more than 0.25 in. (6 mm) from the concrete surface. Dry
abrasive blasting will produce large quantities of airborne
particulates, such as dust, and precautions should be taken to
protect personnel and equipment in the work area.
3.3.2.1.1.2 Wet sandblasting—In wet sandblasting, the free
particulate rebound that results from the sand being projected
at the concrete surface is confined within a circle of water.
Although this process reduces the amount of airborne partic-
American Concrete Institute – Copyrighted © Material – www.concrete.org
16
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 3.3.2.1.2—Shotblasting.
ulates, some of the water intercepts the sand being projected
at the concrete surface and reduces the efficiency of the abrasive blasting operation to effectively remove concrete and
provide surface profile. This process is generally limited to
cleaning a concrete surface or reinforcing steel.
3.3.2.1.1.3 Low-pressure water blasting with abrasives—
Low-pressure water blasting with abrasives is a cleaning
system using a stream of water at low pressure (1500 to 5000
psi [10 to 35 MPa]) with an abrasive such as sand, aluminum
oxide, or garnet, introduced into the stream. This equipment can remove dirt or other foreign particles and concrete
laitance, thereby exposing the fine aggregate and leaving the
concrete surface clean and free of dust.
This method eliminates airborne particles that normally
occur when using dry/wet abrasive blasting procedures. The
water used is collected and the abrasive removed before the
water is discharged into a wastewater system.
3.3.2.1.2 Shotblasting—Shotblasting equipment cleans
and removes concrete by projecting steel shot at the concrete
surface at high velocity within an enclosed blast chamber
that recovers and separates most of the dust and reusable shot
(Fig. 3.3.2.1.2). The shot erodes and pulverizes the concrete
at the surface. The depth of removal is controlled by shot
size, machine setup, and rate of travel. The shot rebounds
with the pulverized concrete and is vacuumed into the body
of the shotblasting machine. The concrete particulates are
separated out and deposited into a holding container to be
discarded later while the shot is reused. The shotblasting
process is a self-contained operation that is highly efficient
and environmentally sound.
Shotblasting uses shot of varying sizes. The final surface
profile required determines the size of the shot and the
speed at which the machine will travel. A surface cleaning
operation is achieved by using smaller (0.017 to 0.028 in.
[0.43 to 0.71 mm] diameter) shot and setting the machine
for maximum travel speed. Concrete removal up to 1/4 in.
(6 mm) is possible in a single pass by increasing the size
of the shot (0.033 to 0.055 in. [0.84 to 1.4 mm] diameter)
and reducing the travel speed. Shotblasting can provide
CSP ranging from CSP2 to CSP8 (ICRI 310.2R), making
this method suitable for roughening horizontal surfaces in
preparation for receiving sealers, coatings, and overlays. It
is also useful for removing existing coatings, adhesives, and
surface contaminants. Hand-held equipment is also available
for use on vertical surfaces.
3.3.2.2 Cleaning methods—Common methods of cleaning
concrete surfaces are discussed in the following.
3.3.2.2.1 Chemical cleaning—In many cases, chemical
cleaning methods of surface preparation are not appropriate
for use with the concrete repair materials and methods
presented in this guide. With certain sealers and coatings
under certain conditions, however, it may be possible to use
detergents, trisodium phosphate, and various proprietary
concrete cleaners to remove dirt, oil, grease, buildup, and
oxidation deposits from concrete surfaces (ASTM D4258).
All traces of the cleaning agent should be removed after
the contaminating material is removed. Solvents should not
be used to clean concrete because they may dissolve the
contaminant and carry it deeper into the concrete.
3.3.2.2.2 Acid etching (ASTM D4259 and D4260)—Acid
etching of concrete surfaces has long been used to remove
laitance and surface concrete. The acid removes cement
paste and provides a slight surface profile by exposing fine
aggregate. This lightly profiled surface promotes penetration and adhesion of sealers and coatings, especially thinfilm coatings. Acid should only be used when no alternative
means of surface preparation can be used. ACI 503R does
not recommend the use of acid etching. Acids may penetrate
the concrete surface through cracks and promote corrosion of underlying reinforcing steel in structural concrete.
The acids can weaken the remaining cement paste on the
concrete surface. Care should be taken to neutralize residual
acid on prepared surfaces (ASTM D4262) and in wastewater.
Thorough removal of etching debris is required to eliminate
bond-inhibiting contaminants on the concrete surface. As
such, large quantities of rinse water, mechanical scrubbing,
and vacuum removal are necessary.
3.3.2.2.3 Low-pressure water cleaning without abrasives—Water is sprayed to remove dirt and loose, friable
material. Using pressures less than 5000 psi (35 MPa), this
method does not remove any significant amount of concrete.
It can be used outdoors or indoors where mist and water
can be tolerated. This method can be used in horizontal,
vertical, or overhead situations. However, it generally does
not produce any significant increase in texture, profile, or
pattern in the concrete and therefore should be a supplement
to other methods in most surface preparation applications
(ICRI 310.2R).
3.3.3 Cleaning reinforcing steel—All exposed surfaces of
the reinforcement should be thoroughly cleaned of all loose
concrete, rust, oil, and other contaminants. Sandblasting is
the preferred method. The degree of cleaning depends on
the repair procedure and material selected. For limited areas,
wire brushing or other hand methods of cleaning may be
acceptable. When cleaning the steel and removing loose
particles from the repair area after cleaning, neither the reinforcing steel nor the concrete substrate should be contaminated with oil from the air compressor. For this reason, either
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
an oil-free compressor or one that has a good oil trap should
be used. High-pressure water blasting is also effective in
cleaning the surface and reinforcing steel. When using
moisture-sensitive repair materials, it will be necessary to
remove any excess water before application of repair material. Saw-cut edges of the repair area should also be abrasive-blasted to roughen the saw cut vertical surface. Refer
to 5.4 for reinforcement repair and 6.7.4 and 6.7.5 for installation of embedded galvanic anodes and cathodic protection
systems to reinforcing steel.
3.3.4 Final cleaning of repair area—Upon completion of
surface preparation and cleaning of the reinforcing steel, the
surface should be clean, dry, and free of microcracking and
bruising. All loose concrete, aggregate, rust, oil, and other
contaminants should be removed from the concrete surface
and reinforcing steel. This may require further sand, water,
or air blasting; vacuuming; or other techniques.
3.4—Quality control and assurance
Quality control and assurance procedures are required
throughout the concrete removal and surface preparation operations. These can be accomplished through visual
inspection, soundings, and use of a covermeter or other
means to locate reinforcement. Sounding is an excellent
means to identify delaminated and debonded concrete;
however, identification of subsurface cracks, microcracking,
and the extent of deterioration or other internal defects may
not be determined by these methods alone. Other means of
evaluation should be used to properly identify the extent of
deteriorated and damaged concrete and to verify its complete
removal in the repair process.
Various evaluation methods (ACI 228.2R and ICRI
210.4) can provide valuable information about the condition of the concrete repair before, during, and after concrete
removal. Some test methods require concrete core samples
from the existing concrete or repair material. More common
test methods and evaluations performed during the repair
process are outlined:
1) Methods for concrete strength
a) Cores and cylinders—compressive, tensile, modulus
of elasticity. and splitting tensile strength
b) Pullout (ASTM C900)
c) Pulse velocity (ASTM C597)
2) Reinforcing steel location
a) Covermeter
b) Ground-penetrating radar (GPR)
c) X-ray
3) Delamination, debonding identification, and microcracking (can be identified by petrographic analysis)
a) Visual examination
b) Acoustic impact (ASTM D4580—includes chain
drag/hammer sounding, electromechanical sounding,
and rotary percussion methods)
c) Impact-echo (ASTM C1383)
d) Infrared thermography (ASTM D4788)
e) Ground-penetrating radar (GPR) (ASTM D6087)
4) Surface cleanliness and strength (ACI 515.1R)
a) Test for pH of cleaned surfaces (ASTM D4262)
17
b) Surface cleaning concrete for coatings (ASTM D4258)
c) Testing by tape lift (ASTM E1216)
5) Measuring surface profile (ICRI 310.2R)
a) Replica putty (ASTM D7682)
b) Replica tape (ASTM D4417)
c) Sand method (ASTM E965)
d) Laser profilimetry
6) Tensile pull-off testing (ASTM C1583, ICRI 210.3)
CHAPTER 4—REPAIR MATERIALS
4.1—Introduction
This chapter describes the various categories of materials
available for repair or rehabilitation of concrete structures.
Typical properties, advantages, disadvantages or limitations,
typical applications, and applicable standards and references
are discussed for each repair material. General guidance on
selecting repair materials is also provided. For more information on selecting repair materials, refer to ACI 546.3R.
4.2—Concrete replacements and overlays
To match the properties of the concrete being repaired as
closely as possible, portland-cement concrete and mortar
or other cementitious compositions using similar proportions of ingredients are typically the best choices for repair
materials. The new cementitious repair material should be
compatible with the existing concrete substrate.
4.2.1 Conventional concrete—Conventional concrete
composed of portland cement, aggregates, and water is often
used as a repair material. Admixtures are used to entrain air,
accelerate or retard hydration, improve workability, reduce
mixing water requirements, increase strength, reduce drying
shrinkage, reduce the potential for corrosion of steel reinforcement, reduce expansion of alkali-aggregate reaction, or
alter other properties of the concrete (ACI 212.3R). Pozzolanic materials such as fly ash, silica fume, granulated blastfurnace slag or other supplementary cementitious materials may be used in conjunction with portland cement for
economy or to provide specific properties such as reduced
early heat of hydration, improved later-age strength development, reduced permeability, or increased resistance to
alkali-aggregate reaction and sulfate attack.
Concrete proportions should be designed to provide the
workability, density, strength, and durability necessary
for the particular application (ACI 211.1). To minimize
shrinkage cracking, the repair concrete should have a watercementitious materials ratio (w/cm) as low as possible and a
coarse aggregate content as high as possible. When proper
restraint is provided, shrinkage-compensating concrete also
contributes to the reduction of drying shrinkage cracking
(ACI 223R). Frost-resistant normalweight concrete should
have a w/cm not exceeding 0.45 for thin sections, such as
1.5 to 3 in. (40 to 75 mm) and 0.50 for greater thicknesses
(ACI 201.2R). Mixing, transporting, and placing of conventional concrete should follow the guidance given in ACI 301,
ACI 304R, ACI 304.1R, ACI 304.2R, ACI 304.5R, and ACI
304.6R.
American Concrete Institute – Copyrighted © Material – www.concrete.org
18
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
4.2.1.1 Advantages—Conventional concrete is readily
available, well understood, economical, has similar properties to the existing concrete, and is relatively easy to produce,
place, finish, and cure. Generally, concrete mixtures can be
proportioned to match the hardened properties of the underlying concrete, making conventional concrete applicable in
a wide range of repairs.
Conventional concrete can be easily placed under water
using a number of familiar techniques and precautions to
ensure the integrity of the concrete after placement (ACI
304R and ACI 546.2R). Concrete is typically placed under
water using a tremie or a pump.
4.2.1.2 Limitations—Conventional concrete should not
be used in repairs where the aggressive environment that
caused the original concrete to deteriorate has not been eliminated, unless an appropriate design mixture for the exposure condition is used or a reduced service life is acceptable.
For example, if the original deterioration was caused by acid
attack, aggressive water attack, or abrasion-erosion, repair
with conventional concrete may not be successful unless the
cause of deterioration is mitigated.
The shrinkage properties of the repair materials are critical because the new repair materials are being placed on an
existing substrate that has likely undergone essentially all
the shrinkage that it will experience. Curing requirements,
as well as the required properties of the repair material,
including strength, modulus of elasticity, and limitations on
maximum shrinkage strain, if needed, should be addressed
by the licensed design professional (LDP) in the repair
specifications.
Concrete that is mixed, transported, and placed under
hot weather conditions, including any combination of high
temperature, low humidity, or wind, requires measures to
be taken to eliminate or minimize undesirable effects (ACI
305R). There are also special requirements for producing and
placing concrete during cold weather conditions (ACI 306R).
4.2.1.3 Applications—Conventional concrete is often
used in repairs involving relatively thick sections and large
volumes of repair material. Typically, conventional concrete
is appropriate for partial- and full-depth repairs and resurfacing overlays where the minimum thickness is greater than
2 in. (50 mm), especially where the overlay extends beyond
the reinforcement, or where the repair area is large. Conventional concrete is commonly used for repairs of slabs, walls,
columns, piers, and hydraulic structures (McDonald 1987),
as well as for full-depth repairs or overlays on bridge or
parking structure decks.
Conventional concrete is particularly suitable for repairs
in marine environments because the typically high humidity
in such environments minimizes the potential for shrinkage
(Troxell et al. 1958).
4.2.1.4 Standards—ASTM C94 covers ready mixed
concrete manufactured and delivered to a purchaser in a
freshly mixed and unhardened state. Properties such as
shrinkage and bond are not addressed in this specification
and should be specified separately.
4.2.2 Conventional mortar—Conventional mortar is
a mixture of portland cement, fine aggregate, and water.
Water-reducing admixtures, supplementary cementitious
materials, expansive components, and other modifiers are
often used with conventional mortar to minimize shrinkage
and adjust other properties.
4.2.2.1 Advantages—The advantages of conventional
mortar are similar to those of conventional concrete, except
that mortar can be placed in thinner sections. A wide variety
of prepackaged mortars are available. They are particularly
appropriate for small repairs.
4.2.2.2 Limitations—Mortars generally exhibit increased
drying shrinkage compared to concrete because of their
higher water volume, higher unit cement content, higher
paste-aggregate ratio, and the absence of coarse aggregate. Proper air entrainment, which is approximately 4 to 6
percent, is often required to provide adequate resistance to
freezing and thawing as well as scale resistance; however,
air content does reduce the strength of the mortar. Prepackaged mortars typically include air-entraining admixtures
(Types IA, IIA, or IIIA).
4.2.2.3 Applications—Conventional mortar should not
be used in many situations when thin repair sections are
required. These applications should be reviewed when
installed in the path of vehicular traffic that is subject to
repetitive loading. Because field conditions affect the development of the performance of mortar, testing for relevant
properties should be performed to closely simulate the application conditions.
4.2.2.4 Standards—ASTM C387 covers the production, properties, packaging, and testing of packaged, dry,
combined materials for mortar and concrete. Special consideration should be given to properties not covered in this
specification, such as shrinkage and durability.
4.2.3 Proprietary concrete and mortars—Proprietary
repair mortars are prepackaged mortars that are a blend of
portland cement or specialty cement; fine aggregate; and
admixtures such as plasticizers, expansive components,
densifiers, accelerators, polymers, thixotropic agents, and
other additives. Depending on the specific use, mortars may
contain variable aggregate gradations for different placement depths and consistencies. Proprietary repair mortars
are also available that are trowelable, sprayable, and specifically intended for overhead or vertical applications. Some
proprietary repair mortars can be extended with coarse
aggregate for deeper application sections.
4.2.3.1 Advantages—The advantages of proprietary repair
materials are convenience of use and the broad range of
products with different physical and mechanical properties to meet different conditions, such as partial-depth
repairs on vertical and overhead surfaces without the need
of forms as well as form-and-pour applications. They often
have faster set times and shorter cure times when compared
with conventional concrete and mortar. They are suitable
for performance-based requirements, as the composition
typically is formulated to achieve published values. The
preblended materials used in proprietary mortars are convenient for small quantity placements where the proportioning
of conventional mortars is inconvenient; difficult to disperse;
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
or too complex for field conditions, such as the quantity of
material used, rapid hardening, or accessibility.
4.2.3.2 Limitations—Proprietary repair mortars may
have different mechanical properties than the concrete
being repaired. In addition, the substrate concrete has likely
already experienced most of its shrinkage and property
development. Because proprietary mortars may be cementrich and use a complex blend of modifiers, they can have a
propensity for high shrinkage compared with conventional
concrete. Shrinkage characteristics can be provided by
the material manufacturer. Although there are no industry
standards specifying bond strength of these mortars, International Concrete Repair Institute (ICRI) 210.3 or ASTM
C1583 tensile bond testing is appropriate for evaluating
in-place bond.
4.2.3.3 Applications—Some proprietary mortars are
recommended for repairs as thin as 1/8 in. (3 mm). Thin
mortar applications should use special products developed for this purpose, especially when installed in the
path of vehicular traffic or subjected to repetitive loadings.
Testing should be performed under actual field conditions to
ensure the satisfactory performance of the material and the
installation.
4.2.3.4 Standards—ASTM C928, the standard specification for packaged, dry, rapid-hardening cementitious
materials for concrete repairs, cautions that chloride levels
greater than 1 lb/yd3 (600 g/m3) of the hardened repair material is indicative that the packaged material contains sufficient chlorides to cause corrosion-to-steel reinforcement
when the concrete is exposed to weather, is on the ground,
or is in a moist environment (ACI 222R). Much lower chloride ion content should be used in prestressed concrete. The
allowable drying shrinkage is up to 0.15 percent at 28 days
according to ASTM C157, although this much shrinkage
or additional drying shrinkage will likely compromise the
integrity of the repair. This standard is not all-inclusive, and
compliance to ASTM C928 is no assurance of the required
suitability or durability of the repair material. The U.S.
Army Corps of Engineers (USACE) UFGS-03 01 32 guide
specifications (USACE 2009) limit unrestrained drying
shrinkage to 0.04 and 0.10 percent at 28 days and ultimate,
respectively, for repair of civil works-type structures. Limits
on restrained shrinkage are also specified. ICRI 320.3R and
ACI 364.3R provide guidance for appropriate tests to determine properties and describe characteristics of proprietary
repair mortars. Information on criteria for selecting proprietary repair mortars can be found in ACI 546.3R.
4.2.4 Cement grouts—Cement grouts are commonly
mixtures of hydraulic cement, fine aggregates, and water that
produce a plastic, flowable or fluid consistency grout. Some
grout formulations do not include all of these components
or provide alternate components to achieve the same type
of final consistency, workability, and strength. Admixtures
are frequently included in the grout to reduce segregation of
the contents, reduce mixing water, accelerate or retard time
of setting, minimize shrinkage, reduce or eliminate bleed,
improve pumpability or workability, or improve the durability of the grout. Fly ash may be used to enhance perfor-
19
mance or reduce cost. Silica fume may be used to increase
chemical resistance, density, durability, and strength while
decreasing permeability. Prepackaged grout compliant with
ASTM C1107 may not be appropriate for some types of
repairs that do not provide restraint or provide proper curing
and should never be modified without the manufacturer’s
approval.
4.2.4.1 Advantages—Cement grouts are economical,
readily available, easy to install, and closely compatible
with concrete. Admixtures can modify cement grouts to
meet specific job requirements. Shrinkage-reducing admixtures and expansive components are available to minimize
shrinkage effects. Non-shrink grouts are also available.
4.2.4.2 Limitations—Cement grouts can be used for
repairs by injection, but only where the width of the opening
is sufficient to accept the solid particles suspended in the
grout. The minimum crack width at the point of introduction
should be approximately 0.25 in. (6 mm).
4.2.4.3 Applications—Typical applications of hydrauliccement grout may vary from grout slurries for bonding old
concrete to new concrete, to filling of large dormant cracks,
or to filling of voids around or under a concrete structure.
Non-shrink cement grouts can be used to repair spalled or
honeycombed concrete or to install anchor bolts in hardened
concrete, but should be used in accordance with the manufacturer’s instructions.
4.2.4.4 Standards—The U.S. Army Corps of Engineers
CRD C621-93 (USACE 1993) covers three grades of packaged, dry, hydraulic-cement grouts (non-shrink) intended for
use under applied load, such as to support a structure or a
machine, where shrinkage is to be minimized.
4.2.5 Polymer-portland-cement concrete and mortar—
Polymer-portland-cement concrete and mortar (PPCC) and
latex-modified concrete (LMC) are identified as portland
cement and aggregate combined, at the time of mixing, with
organic polymers dispersed or redispersed in water. This
dispersion is called a latex, where the organic polymer is
a substance composed of thousands of simple molecules
combined into large molecules. The simple molecules are
known as monomers, and the reaction that combines them is
called polymerization. The polymer may be a homopolymer
if it is made by the polymerization of one monomer, or a
copolymer if two or more monomers are polymerized.
Polymer dispersions are added to the concrete mixture to
improve the properties of the final product. These properties include improved bond strength to concrete substrates,
increased flexibility and impact resistance, improved resistance to penetration by water and by dissolved salts, and
improved resistance to freezing and thawing.
Of the wide variety of polymers investigated for use in
PPCC, polymers made by emulsion polymerization have
been the most widely used and accepted (ACI 548.3R).
Styrene butadiene and acrylic latexes have been the most
effective and predictable for concrete restoration. Other
commonly used latexes include polymers and copolymers of
vinyl acetate with ethylene (VAE) or other vinyl monomers
such as vinyl versatate.
American Concrete Institute – Copyrighted © Material – www.concrete.org
20
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
When emulsified and mixed with concrete, epoxies
provide excellent resistance to freezing and thawing,
reduced permeability, and improved chemical resistance.
The bond of epoxies is excellent whereas flexural, compressive, and tensile strengths can be high. Epoxy emulsions,
however, have had limited use in concrete due to the desire
to use repair materials with physical properties similar to the
substrate.
Mixture proportions depend on the specific application
and the type of polymer used in the PPCC. Levels of 10 to
20 percent polymer solids by mass of cement are required
for most applications. Typical w/cm for workable PPCC
mixtures used for repair range from 0.30 to 0.40 for mixtures
containing latexes, and 0.25 to 0.35 for mixtures containing
epoxies (ACI 548.1R). While latex polymers are used almost
exclusively for PPCC overlays, redispersible polymer
powders have been used as well. However, these polymer
powders are used more commonly in repair situations.
4.2.5.1 Advantages—Polymer-portland cement concrete
overlays have exhibited excellent long-term performance.
Properly installed overlays are highly resistant to freezingand-thawing damage, and they exhibit minimal bond failure
after many years of service. Latex-modified concrete overlays installed on severely deteriorated bridge decks after
proper surface preparation continue to perform many years
after installation. Reports of satisfactory long-term performance on structures of variable initial condition and harsh
in-service exposure are common (Virginia Transportation
Research Council 2001).
The bonding characteristics of PPCC are excellent (Kuhlmann 1990), and PMC typically exhibits low permeability
(Kuhlmann 1984).
Styrene-butadiene PPCC has excellent durability for exterior exposures or environments where moisture is present.
4.2.5.2 Limitations—Polymer-portland-cement concrete
should be placed and cured at 45 to 85°F (7 to 30°C) with
special precautions taken when either extreme is reached
(ACI 548.1R; ACI 306.1).
Handling and finishing PPCC is limited to less than 30
minutes; therefore, mobile volumetric mixers fitted with
an additional storage tank for the latex should be used for
large applications of LMC. When small batches are mixed
in drum or mortar mixers, the mixing time should be limited
to 3 minutes. Longer mixing times result in an increase in
total air content with subsequent reductions in compressive
strength. Latex-modified concrete has a tendency for plastic
shrinkage cracking during field placement. Special precautions are necessary when the evaporation rate exceeds 0.1 lb/
ft2/h (0.5 kg/m2/h) (ACI 308R; ACI 548.4).
The modulus of elasticity is generally lower compared to
conventional concrete; therefore, its use in vertical or axially
loaded members should be carefully evaluated (Kuhlmann
1990).
Polyvinyl acetate should not be used in applications that
may be exposed to moisture.
Epoxy emulsions are more expensive than most latexes,
and some are susceptible to color change and deterioration
from exposure to sunlight. Surface discoloration occurs
when the concrete is exposed to UV light. Where such
discoloration is not acceptable, acrylic polymers should be
used.
4.2.5.3 Applications—Polymer-portland-cement concrete
applications include overlays of bridge decks, parking structures, and decks, as well as repair of any concrete surfaces.
Styrene butadiene latex is commonly used for repair of
bridges, parking decks, and floors. Acrylic latexes are used
for floor repair and are particularly suitable in exterior white
cement applications where color retention is important.
Polymer-portland-cement concrete is most commonly
used for overlays and is normally applied in sections ranging
from 1.5 to 4 in. (40 to 100 mm) thick for concrete and 0.75
to 1.5 in. (20 to 40 mm) for mortars. These systems restore
lost sections and provide a new high-strength wearing
surface that is very durable against weathering and can be
placed into service when it has developed sufficient strength,
which is dependent upon the hydration of the cement.
Although mainly used as overlay materials, PPCC is also
an effective repair material. Typically, PPCC repairs are
relatively shallow; therefore, mixture proportions similar to
those shown in ACI 548.3R should be considered.
4.2.5.4 Standards—ASTM C685 covers concrete made
from materials continuously batched by volume and mixed
in a volumetric mixer. Tests and criteria for batching accuracy and mixing efficiency are specified. ACI 548.4 covers
the placement of styrene-butadiene LMC overlays for bridge
decks. ASTM C1438 covers latex and redispersible polymer
powder modifiers, and ASTM C1439 covers test methods for
PPCC. ACI 548.1R includes a bibliography of major references covering polymers in concrete and a glossary of terms.
4.2.6 Polymer concrete and mortar—Polymer concrete
and mortar (PC) is a composite material in which the aggregate is bound together in a dense matrix with a polymer
binder. The composites do not contain a hydrated cement
phase, although portland cement can be used as an aggregate or filler. The term “PC” should never suggest a single
product but rather a family of products. Use of the term “PC”
in this section also includes mortar.
Polymer concrete and mortar has been made with a variety
of resins and monomers, including polyester, epoxy, furan,
vinylester, high-molecular-weight methacrylates (HMWM),
and styrene (ACI 548.1R). Polyester resins are desirable
because of moderate cost, availability of a great variety
of formulations, and relatively good PC properties. Furan
resins are low cost and highly resistant to chemical attack.
Epoxy resins are generally higher in cost, but may offer
advantages such as low shrinkage, and some formulations
bond to damp surfaces without requiring a primer. ACI 503R
provides information on the use of epoxy compounds with
concrete. A special form of PC is sulfur concrete, which is
placed hot and is thermoplastic. For further information,
refer to ACI 548.2R.
The properties of PC depend on the properties and the
amount of the polymer used, modified somewhat by the
effects of the aggregate and the filler materials. Typically,
PC mixtures exhibit rapid curing; high tensile, flexural, and
compressive strengths; good adhesion to most surfaces; good
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
resistance to freezing and thawing; low permeability to water
and aggressive solutions; and good chemical resistance.
4.2.6.1 Advantages—PC can provide a fast-curing, highstrength repair material that is suitable for repair of PCC
structures. PC is mixed, placed, and consolidated in a
manner that is similar to conventional concrete. With some
formulations, external vibration is required.
A wide variety of prepackaged polymer mortars is available that can be used as mortars or added to selected blends
of aggregates. Depending on the specific use, mortars may
contain variable aggregate gradations intended to impart
unique surface properties or aesthetic effects to the structure
being repaired. Polymer mortars that are trowelable, specifically intended for overhead or vertical applications, or both,
are also available.
Epoxy mortars shrink less than polyester or acrylic
mortars. Shrinkage of polyester and acrylic mortars can be
reduced by using an optimum aggregate loading. The aggregate grading and the mixture proportions should be available
from the polymer formulator.
Polymer mortars are ideally suited for thin repairs and
overlays less than 0.75 in. (20 mm).
4.2.6.2 Limitations—Organic solvents are required to
clean equipment when using polyesters and some epoxies.
Manufacturers should be consulted before using proprietary
materials to address the issue of volatile organic compound
(VOC) restrictions. Epoxy materials are also sensitizers
capable of causing allergic reactions and other health hazards.
The disposal of epoxy materials that are unreacted may also
be classified as hazardous waste in some areas and should
therefore be done in accordance with local ordinances.
Rapid curing generally means less time for placing and
finishing operations. Working times for these materials are
variable and, depending on ambient temperatures, may range
from less than 15 minutes to more than 1 hour. Ambient and
concrete temperatures may affect polymer viscosity, cure
time, or performance.
The coefficients of thermal expansion of polymer materials vary from one product to another and are higher than
conventional concrete.
Shrinkage characteristics of PCs should be closely evaluated so that unnecessary shrinkage cracking is avoided.
The modulus of elasticity of PC is lower than that of
conventional concrete, especially at higher temperatures.
Its use in load-carrying members should be carefully
considered.
Only a limited number of polymer systems are appropriate
for repair of wet, damp, or moist concrete surfaces. The
aggregates used in PC should be dry to obtain the highest
strengths and ensure the integrity of the concrete or mortar.
High temperatures can adversely affect the physical properties of certain PC, causing softening. Service temperatures
should be evaluated before selecting PC systems for such
use. Epoxy systems may burn in fires where temperatures
exceed 450°F (230°C) and can soften at lower temperatures.
Users of PC should consider its lack of fire resistance.
Conventional concrete generally does not bond to cured
PC, unless the aggregate is exposed and free of any polymer.
21
4.2.6.3 Applications—PC repair materials are designed for
the repair of a broad variety of conditions that allow closing
of a repair area for only a few hours. PCs are not limited to
that use, however, and can be formulated for a wide variety
of applications, provided consideration is given to the
modulus, creep, thermal, and other properties of a specific
product.
PC is used in several types of applications—fast-curing,
high-strength repair of structures, and thin 0.1 to 0.75 in. (3
to 19 mm) overlays for floors and bridge decks.
Polymer mortars have been used in a variety of repairs
where only thin sections, such as overlays, are required.
Polymers with high elongation and low modulus of elasticity
are particularly suited for bridge overlays.
PC overlays are especially well suited for use in areas
where concrete is subject to chemical attack.
For exterior applications, PCs using a preplaced aggregate
procedure have been successfully used in large volumes
with cross sections greater than 1 ft2 (0.1 m2) and greater
than 15 ft (4.5 m) in length (Project Profile 1993).
4.2.6.4 Standards—ACI 503.4 is a specification for repair
of defects in hardened PCC with a sand-filled mortar using
an adhesive binder as defined in ASTM C881. It includes
requirements for adhesive labeling, storage, handling,
mixing and application, surface evaluation and preparation,
and inspection and quality control.
ASTM C881 covers two-component, epoxy-resin bonding
systems for application to PCC, which are able to cure under
humid conditions and bond to damp surfaces.
4.2.7 Magnesium phosphate concrete and mortar—
Magnesium phosphate concrete and mortar (MPC) is based
on a hydraulic cement system that is different from portland
cement. Unlike portland cement and some polymer-cement
concrete, which require moist curing for optimum property
development, these systems produce their best properties
upon air curing, similar to epoxy concrete. Rapid strength
development and heat are produced, although retarded
versions are available that produce less heat. These materials
have been used in repairs to concrete since the mid-1970s.
4.2.7.1 Advantages—Magnesium phosphate concrete
and mortar is typically classified as ultra-rapid hardening
(Type URH) cement. This classification requires a minimum
compressive strength of 3000 psi (21 MPa) at 1.5 hours and
a maximum 28-day drying shrinkage of 0.07 percent (ASTM
C1600). Retarded versions with extended setting times of 45
to 60 minutes at room temperature are also available. Scaling
resistance is similar to air-entrained, portland-cement-based
concrete materials. When extended with aggregates, abrasion resistance of MPC is similar to conventional concrete
of similar strength when tested in accordance with ASTM
C672. Neat magnesium phosphate cement naturally has
lower abrasion resistance similar to portland-cement mortar
of equal strength.
Magnesium phosphate mortar and concrete can be placed
at temperatures as low as 32°F (0°C), or lower if the mixing
water and material are heated. Magnesium phosphate
mortars typically achieve 6000 psi (40 MPa) compressive
strength within 48 hours and do not increase much beyond
American Concrete Institute – Copyrighted © Material – www.concrete.org
22
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
that level. The material has good bond strength to portland
cement and low permeability. Thin repairs with magnesium
phosphate mortar often have improved performance when
compared with portland cement repairs because they generally do not require a moist cure.
4.2.7.2 Limitations—Magnesium phosphate concrete
and mortar should be extended only with noncalcareous
aggregates such as silica, basalt, granite, trap rock, and
other hard rocks. Reaction of carbonated surfaces with the
early-forming phosphoric acid produces carbon dioxide
(CO2) and weakens the paste aggregate bond. Because of
its acid-base reaction, MPC should be used only on wellprepared concrete substrates that have had the carbonation
layer removed by mechanical or chemical means. Magnesium phosphate concrete and mortar reacts chemically with
the dust of the fracture, sawing residue, portland cement
contamination, or carbonated zone in the concrete and can
cause a reduction in bond strength at the bond interface.
Careful attention should be paid to surface preparation
and drying times of MPC if impermeable membranes are to
be applied over it. The MPC and membrane manufacturers
should be contacted for recommendations.
Because of the short time between initial and final setting
times, MPC is generally not hard troweled.
The field technician does not have the flexibility of varying
the water content and, therefore, MPC cannot be placed in
a dry-pack consistency. The mixing water typically has a
tolerance of only ±10 percent. Any variation of the water
content from that specified by the manufacturer reduces both
the strength and the durability of the MPC mortar.
The neat or extended magnesium phosphate mortar
develops a very rapid exothermic reaction that can produce
relatively high temperatures. Typically, the mortar should
not be placed at temperatures above 80°F (27°C) or in the
sunlight within the temperature ranges of 60 to 80°F (15 to
27°C). However, hot and cold weather formulas are available and may have different temperature ranges. The manufacturer should be consulted for temperature ranges and
when placing the material in thickness greater than 4 in. (100
mm) or in insulated cavities where the heat generated cannot
escape. Extending the mixture with aggregates or using cool
water can slow down the exothermic reaction.
As it hardens, MPC quickly produces high strength and a
high modulus of elasticity. Therefore, MPC lacks the flexibility and toughness that is typically found with organicmodified mortars and is susceptible to fracturing from
impact loads.
With the normal setting formulations of MPC, high heat
peaks are encountered. With sustained exposure to temperatures in excess of 180°F (80°C) in service, strength reductions can develop, but its compressive strength can be
expected to exceed that of normal concrete.
4.2.7.3 Applications—Repair applications are the most
common use of MPC, and are cost-effective for rapid repairs
where a short downtime is important. Common uses are in
highway, bridge deck, airport, tunnel, and industrial repairs.
Repairs in a cold-weather environment are important
applications. Due to the exothermic nature of the reac-
tion, heating the materials and the substrates is not typically necessary unless the temperature is below 32°F (0°C).
Magnesium phosphate concrete and mortar is useful for
cold-weather embedments and anchoring because of its high
bond strength and low shrinkage rate.
4.2.8 Supplementary cementitious materials—In addition
to the information provided in this section, ACI 232.1R, ACI
232.2R, and ACI 234R may also be consulted.
4.2.8.1 Silica-fume concrete—Silica fume (ASTM
C1240), categorized as a supplementary cementitious material, is a very fine noncrystalline silica and by-product in
the manufacture of silicon and ferrosilicon alloys. It is an
efficient pozzolanic material that enhances mechanical and
durability properties of concrete. Silica fume is normally
added to concrete in quantities of 5 to 15 percent by weight
of cement, reducing the amount of cement used in a given
mixture. Silica fume is available in several forms, as a slurry,
densified (compacted), and pelletized.
4.2.8.1.1 Advantages—In general, the addition of silicafume to concrete increases compressive and bond strength,
decreases permeability, and produces a concrete that is more
resistant to abrasion and attack from sodium sulfate and
some chemicals (ACI 234R). When used in sufficient quantity and properly dispersed, it can be an effective means of
mitigating alkali-silica reaction (ASR) in concrete. Silicafume concrete requires no significant changes from the
normal transporting, placing, and consolidating practices
associated with conventional concrete. Silica-fume concrete
is more cohesive and thus, less prone to segregation. It
also exhibits little or no bleeding for improved durability.
Without bleeding, finishing operations can be continuous
from placement to texturing and curing, taking less time
for finishing. Silica-fume concrete can also produce higher
early age strengths, lessening the time required to strip forms
and tension prestressing steel in structures. It is also possible
that coatings can be applied sooner on silica-fume concrete
than conventional concrete.
4.2.8.1.2 Limitations—Because silica-fume concrete is
more susceptible to plastic shrinkage cracking, exhibiting
significantly reduced bleeding, special attention to curing
and protection is necessary to prevent cracking. Additionally, plastic silica-fume concrete tends to be sticky, making
it more difficult to finish; however, finishers have overcome
this condition without any significant difficulties (Holland
1987). Because silica fume concrete has little or no bleed
water, it makes it difficult to provide a steel trowel finish.
Hardened concrete containing silica-fume is generally
darker than conventional concrete, and may not blend well
with the appearance of the adjacent existing concrete. The
addition of silica-fume adds cost to the repair material.
4.2.8.1.3 Applications—The first major applications of
silica fume concrete in the United States were for the repair
of hydraulic structures subjected to abrasion-erosion damage
(Holland and Gutschow 1987). The high strength of silica
fume concrete and the resulting abrasion-erosion resistance
offer an economical solution to abrasion erosion problems,
particularly in areas where locally available aggregate may
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
otherwise result in unacceptable concrete for abrasionerosion resistance.
Silica fume concrete is currently widely used to produce
high-performance concrete. Additionally, it is used for corrosion protection in parking structures and bridges, both castin-place and precast. Another application is as an admixture
for shotcrete to reduce rebound loss, increase placement
thickness, and improve durability.
4.2.8.1.4 Standards—ASTM C1240 is the specification
covering silica fume.
4.2.8.2 Shrinkage-compensating cement—Shrinkagecompensating cement is used in concrete to minimize
cracking caused by drying shrinkage. The basic materials
and methods are similar to those used to produce highquality PCC. Consequently, the characteristics of shrinkagecompensating concrete are, in most respects, similar to
those of portland-cement concrete. Proprietary, prepackaged mortar that uses some form of shrinkage-compensating
cement or expansive component to counteract potential
shrinkage is available and has been used successfully for
years. For definitions of expansive cement and expansive
component types G, K, M, and S, refer to ACI 223R.
4.2.8.2.1 Advantages—Ideally, unrestrained shrinkagecompensating concrete will expand by an amount equal
to or slightly greater than the drying shrinkage. Generally, however, reinforcement or external supports result
in restraint, which initially causes compressive stresses in
the concrete. These stresses are subsequently relieved by
drying shrinkage, but are of sufficient magnitude to prevent
cracking. The joints used to control shrinkage cracking can
be reduced or eliminated along with the normal provisions
for waterstops and load-transfer mechanisms. Where a
watertight condition is essential, however, the elimination of
waterstops is not recommended.
4.2.8.2.2 Limitations—Although its characteristics are
similar to those of portland-cement concrete, the materials,
selection of proportions, placement, and curing should be
such that sufficient expansion, compressive stresses, or both,
are obtained to compensate for subsequent drying shrinkage.
The criteria and practices necessary to ensure that expansion occurs at the time and in the amount required are given
in ACI 223R. Low curing temperatures can reduce expansion, so water-curing at moderate temperatures for at least 7
days is essential for the development of the designed expansion. Consult with the manufacturer to determine the need
for any special cleaning of transit mixer drums to prevent
contamination.
Provisions should be made to allow for initial expansion
of the material to provide positive strain on the internal steel
restraint. Other types of restraint, such as adjacent structural
elements, integral abutments, and subgrade friction also
provide restraint and produce compression in the concrete.
Provisions need to be taken to assure an expansion coefficient higher than that of shrinkage in order to avoid cracking
from drying shrinkage. The forces created during the expansion process could push out walls or fail the forms along the
perimeter of the pours.
23
4.2.8.2.3 Applications—Shrinkage-compensating concrete
minimizes cracking caused by drying shrinkage in concrete
slabs, pavements, bridge decks, and structures. Additionally, shrinkage-compensating concrete can reduce warping
tendencies where concrete is exposed to single-face drying
and carbonation shrinkage.
4.2.8.2.4 Standards—ASTM C845 provides standards
and limits for expansive hydraulic cement and expansive
components, including strength, setting time, and expansion. Mortar and concrete expansion is typically determined
in accordance with ASTM C806 and C878, respectively.
Guidelines for the use of shrinkage-compensating concrete
are outlined in ACI 223R.
4.2.8.3 Rapid-setting cements—Rapid-setting cementitious materials are characterized by faster setting times than
conventional cements, as defined by ASTM C1600. Some
may exhibit rapid strength development with compressive
strengths in excess of 3000 psi (21 MPa) in 1-1/2 hours.
4.2.8.3.1 Advantages—Rapid-setting cements provide
accelerated strength development that allows the repair to
be placed into service more quickly than conventional repair
materials. This advantage is important in repairing highways, bridges, airport runways, and industrial plants because
of reduced protection times, lower traffic-control costs,
and improved safety. Some rapid-setting cements provide
significant reduction in shrinkage and increase durability in
sulfate exposures and with reactive aggregates.
4.2.8.3.2 Limitations—Although most rapid-setting materials are as durable as normal portland-cement concrete,
some, due to their constituents, may not perform well in a
specific service environment. Rapid-setting cement systems
are varied and should be evaluated for suitability in the
intended application.
Some rapid-setting materials obtain their strength development, expansive properties, or both, from the formation
of ettringite. If the level of expansion is high and the time
to attain the maximum levels of expansion is long, strength
retrogression may occur. The potential for delayed expansion resulting from insufficient initial curing followed by
rewetting should be recognized.
Some rapid-setting materials are gypsum-based and may
not have long-term durability in wet environments.
Because some of these materials may contain abnormally
high levels of alkali or aluminate to provide expansion,
their exposure to sulfates and reactive aggregates should be
limited. The specifying engineer should review appropriate
application and compatibility issues.
4.2.8.3.3 Applications—Rapid-setting cements are especially useful in repair situations where an early return to
traffic is required, such as repair of pavements, bridge decks,
airport runways, and industrial plants.
4.2.8.3.4 Standards—ASTM C1600 covers performance
requirements for rapid-hardening hydraulic cements.
They are classified as URH, very-rapid hardening (VRH),
medium-rapid hardening (MRH), or general-rapid hardening (GRH) based on setting time, compressive strength,
and other specific criteria. There are no restrictions on the
compositions of the cement or its constituents. Cements
American Concrete Institute – Copyrighted © Material – www.concrete.org
24
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
are classified based on specific requirements for very early
compressive strength development such as time of setting,
compressive strength, and other test methods. As mentioned
in 4.2.8.3.2, some rapid-setting cements may not perform
well in specific service environments. The standard and
optional physical requirements of ASTM C1600 are valuable in determining the suitability of a rapid-setting cement
for specific applications. ASTM C928 covers packaged, dry,
cementitious mortar or concrete materials for rapid repairs to
hardened hydraulic-cement concrete pavements and structures. Use caution to check on exposure conditions, such as
sulfate exposure and alkali reactivity, that are not covered
in the specification. Therefore, additional testing should be
performed at anticipated application temperatures to verify
if properties not covered in the specification are important
for a given project. Advances in the compounding of rapidsetting cements have taken place in recent years.
4.2.9 Common admixtures—ASTM C125 defines an
admixture as “a material other than water, aggregates,
hydraulic cementitious material, and fiber reinforcement that
is used as an ingredient of a cementitious mixture to modify
its freshly mixed, setting, or hardened properties and that is
added to the batch before or during its mixing.”
4.2.9.1 Accelerating admixtures—Accelerators increase
the rate of hydration of hydraulic cement in concrete or
mortar, shortening the set time, increasing the rate of
strength development, or both. Accelerating admixtures
used in concrete should meet the requirements of ASTM
C494, Type C or E.
4.2.9.1.1 Advantages—Accelerators are useful for modifying the properties of concrete or mortar, particularly in
cold weather, to expedite finishing operations, reduce the
time required for proper curing and protection, and increase
the rate of early-strength development to permit earlier
removal of forms and earlier opening of construction (ACI
212.3R). Using accelerators in cold-weather concrete typically is not sufficient to counteract effects of low temperature, and should be combined with cold-weather concreting
practices (refer to ACI 306R).
4.2.9.1.2 Limitations—Accelerating admixtures should
not be considered anti-freeze, because at normal dosages,
accelerating admixtures lower the freezing point of water
in concrete by just 4°F (2°C). Significant lowering of the
freezing point of water requires very high dosages of accelerators, which can cause undesirable side effects. One of
the major disadvantages of calcium chloride accelerators is
that it can cause corrosion of steel reinforcement embedded
in the concrete or repair material when in the presence of
sufficient moisture and oxygen. Non-chloride accelerators
should be used when the potential for corrosion is present.
4.2.9.1.3 Applications—Both chloride and non-chloride
accelerators are used in concrete or mortar applications in
cold weather, or whenever a fast set and strength gain is
required.
4.2.9.1.4 Standards—ASTM C494 and D98 cover material
to be used as chemical-accelerating admixtures and added to
cementitious mixtures in the field.
4.2.9.2 Retarding admixtures—Retarders are admixtures
that delay the setting of the cement paste and reduce the rate
of hydration in concrete. Retarding action is achieved by the
addition of sugar, carbohydrate derivatives, soluble salts and
borates, or methanol to the concrete mixture.
4.2.9.2.1 Advantages—Retarding admixtures are used to
decrease slump loss and extend workability, especially in
hot weather, to ease placement and finishing of concrete.
4.2.9.2.2 Limitations—Retarders generally reduce the
strength of concrete at an early age. If excessive quantities
of retarders are used, they can totally prohibit the setting
of the concrete or otherwise impart undesirable properties.
Results are also dependent on when the retarder is added to
the mixture.
4.2.9.2.3 Applications—Retarders are often used when
placing concrete in hot weather when the normal setting
time is shortened, during difficult placement, mass-concrete
pours, or when placing concrete that requires a unique
finishing technique such as exposed aggregate. Often in
exposed aggregate finishing, retarders are applied to the
interior face of formwork before placement so that the hardening of the cement on the formwork is delayed. This allows
the cement adjacent to the formwork to be removed more
easily to obtain the desired exposed-aggregate finish.
4.2.9.2.4 Standards—ASTM C494 covers material to
be used as chemical-retarding admixtures and added to
cementitious mixtures in the field.
4.2.9.3 Water-reducing admixtures—Water-reducing
admixtures (WRAs) are chemical admixtures that, when
added to cementitious materials such as concrete or mortars,
release the water entrapped between the cement particles and
make it available to increase the workability of the mixture.
They are available in both liquid and powder form. Waterreducing admixtures used in prebagged repair materials are
typically in powder form and those used for concrete production are typically in liquid form. Water-reducing admixtures
used in cement mortars or concrete should meet the requirements of ASTM C494, Type A, D, E, F, or G. Depending
on their water-reducing capacity, WRAs can be classified as
water-reducing admixtures (Types A, D, or E) or HRWRA
(Types F or G). For more information on WRAs, refer to
ACI 212.3R.
4.2.9.3.1 Advantages—WRAs are used in cementitious
concrete or mortars for three primary reasons: 1) to increase
the workability at the same w/cm; 2) to increase strength by
reducing the w/cm at the same workability; or 3) to optimize the cementitious content by keeping the workability
and w/cm the same. Typically, a combination of all three
benefits is taken during concrete or mortar mixture design
proportioning.
Increased workability allows the concrete or mortar to
be placed easily, especially in confined spaces. Reducing
the w/cm allows increasing the strength and durability of
the concrete or mortar without compromising workability.
Cement optimization allows controlling the heat generated
during the heat of hydration of cement, and also allows
lowering the cost of the cementitious mixture.
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
4.2.9.3.2 Limitations—Adding the correct amount of
WRA in cementitious mixtures is important; a dosage rate
that is too high can cause problems such as bleeding, segregation, or extension of set time. A dosage rate that is too low
can result in reduced workability which can prevent proper
placement of the mixture. Some WRAs can also cause an
increase in the air content of the mixture.
4.2.9.3.3 Applications—Water-reducing admixtures are
used for concrete production in the ready-mix, precast, and
dry-cast industry, and in on-site or mobile concrete plants.
Water-reducing admixtures are also used in prebagged
cementitious mortars or concrete. High-range waterreducing admixtures are an important constituent of selfconsolidating concrete (SCC). However, aggregate proportioning and other mixture constituents are also important
design considerations for SCC (ACI 237R).
4.2.9.3.4 Standards—ASTM C494 covers material to be
used as chemical water-reducing admixtures and added to
cementitious mixtures in the field..
4.2.9.4 Corrosion-inhibiting admixtures—Several classifications of corrosion-inhibiting admixtures are available.
They can be generally grouped into three types: cathodic,
anodic, and ambiotic (or mixed) inhibitors, depending on
their area of activity on the corroding steel. Cathodic inhibitors act to prevent the reaction at the cathode. Cathodic
inhibitors act indirectly because they do not prevent metal
dissolution. Anodic inhibitors reduce the rate of reaction at
the anode. They typically react with the corrosion products
to form a protective coating on the metal surface. Nitritebased corrosion inhibitors are one common type of anodic
inhibitor. Mixed inhibitors influence both the anodic and
the cathodic sites that are claimed to be advantageous in
reinforced concrete due to the prominence of microcell
corrosion.
Inhibitors are classified by the Strategic Highway Research
Program SHRP-S-666 (Al-Qadi et al. 1992) as adsorbed
layer formers, oxidizing inhibitors, passivators, conversion
layer formers, and scavengers. Adsorbed layer formers are
organic inhibitors that strongly adsorb to the metal surface
and interfere with the anodic or cathodic reactions in the area
of adsorption. Nitrogen is typically the active atom in an
adsorbed layer inhibitor acting in a non-acid electrolyte on
steel. Typical compounds of nitrogen used as inhibitors are
organic nitrate and amines. Vapor phase inhibitors (VPIs) or
volatile corrosion inhibitors (VCIs) are similar to adsorbed
layer inhibitors. Vapor phase inhibitors are secondary electrolyte layer inhibitors that possess appreciable saturated
vapor pressures under atmospheric conditions, thus allowing
significant vapor phase transport of the inhibitive substance.
Aliphatic and cyclic amines and nitrites with a high vapor
pressure typically make up these inhibitors. Vapor phase
inhibitors\volatile corrosion inhibitors can be added to
cementitious materials as admixtures and be used as SACI.
Oxidizing inhibitors or passivators are another form of
barrier inhibitor that act by shifting the electrochemical
potential of the corroding metal such that an insoluble oxide
or hydroxide forms on the metal surface. Sodium nitrite and
chromates are examples of this inhibitor. Another form of
25
passivators is metal soaps that are a form of the basic alkali
and oxidation products of oil and that form passivating films
on the metal surface. Conversion layer inhibitors form insoluble compounds on metal surfaces without oxidation. In
neutral or basic solution, the presence of calcium and magnesium ions inhibits corrosion by the formation of an insoluble
calcareous scale on the metal surface. Finally, scavengers
act as neutralizing inhibitors by removing concentrations of
corrosive materials such as chloride ion.
The National Association of Corrosion Engineers (NACE)
classifies all corrosion inhibitors, not just those specific to
concrete applications, as passivating inhibitors, cathodic
inhibitors, organic inhibitors, precipitation inhibitors, and
VCIs. Passivating inhibitors cause a large anodic shift of
the corrosion potential, forcing the metallic surface into
the passivation range and are further divided into oxidizing
anions and non-oxidizing ion types. Cathodic inhibitors
either slow the cathodic reaction itself or selectively precipitate on cathodic areas to increase the surface impedance and
limit the diffusion of reducible species to these areas, and
are further classified as cathodic poisons and oxygen scavengers. Organic inhibitors can show both anodic and cathodic
effects but, as a general rule, affect the entire surface of a
corroding metal when present in sufficient concentration.
Organic inhibitors are typically designated as film-forming,
to protect the metal by forming a hydrophobic film on the
metal surface. Precipitation-inducing inhibitors are filmforming compounds that also have a general action over
the metal surface, blocking both anodic and cathodic sites
indirectly by forming a precipitated deposit on the surface
of the metal to provide a protective film. Volatile corrosion
inhibitors and VPIs are compounds transported in a closed
environment to the site of corrosion by volatilization from a
source. On contact with the metal surface, the vapor of VCI
salts condenses and is hydrolyzed by moisture to liberate
protective ions.
4.2.9.4.1 Advantages—Corrosion inhibitors used as
admixtures can be precisely controlled for dosage, pretested
for compatibility in the material, and, once used, are in intimate contact with the steel to be protected. Surface-applied
corrosion inhibitors (SACIs) for hardened concrete are
intended to penetrate into the concrete to reduce corrosion
activity.
4.2.9.4.2 Limitations—The effectiveness of corrosion
inhibitors depends on their concentration. The required
amount of corrosion inhibitor is a function of the level of
corrosion activity. Anodic inhibitors can increase the rate of
attack in unprotected areas (Al-Qadi et al. 1992), similar to
the haloing effect that is sometimes produced around repairs
due to the increase in the cathodic area after repair. Because
of this concentration dependency and effects on adjacent
areas—that is, areas that have received insufficient concentrations—inhibitors with these properties are sometimes
called dangerous, as they may accelerate corrosion.
Most corrosion inhibitors are water-soluble with some
inhibitors also being volatile; therefore, the concentration
of inhibitor may change with time. The corrosion activity
will also change as concrete deterioration occurs, chlo-
American Concrete Institute – Copyrighted © Material – www.concrete.org
26
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
ride ions ingress, and carbonation occurs that may require
a higher concentration of inhibitor than what is within the
concrete. Corrosion is also a complex series of electrochemical processes in a changing environment that can produce
varying results with inhibitors in field conditions.
No standards exist to specifically address SACIs and VCIs
for concrete, with much of the literature presenting differing
opinions about their effectiveness.
4.2.9.4.3 Applications—Another classification of corrosion inhibitors is in terms of application. Inhibitors are either
admixed with the concrete or repair material as an ingredient,
or can be applied to hardened concrete surfaces, relying on
penetration to reach the reinforcing steel surface.
4.2.9.4.4 Standards—ACI 212.3R discusses miscellaneous admixtures for concrete, including corrosion-inhibiting admixtures. ASTM C1582 is a specification for admixtures used as corrosion inhibitors. ASTM G109 is a widely
used test method for evaluating the effectiveness of corrosion-inhibiting admixtures, and various modifications have
been used for SACI and VCI types.
4.2.9.5 Lithium-based admixtures—Various lithium
compounds (Li2CO3, LiOH, Li2SO4) are used in the
formulation of set accelerators for calcium-aluminatecement concrete, and both lithium hydroxide monohydrate
(LiOH·H2O) and lithium nitrate (LiNO3) have been used
to control alkali-silica reactivity (ASR) in portland-cement
concrete. Lithium admixtures consist of water-soluble
salts and are used in high-alkali concrete containing reactive aggregates to inhibit and control ASR. For an in-depth
discussion of the chemistry related to ASR, refer to FHWAHRT-06-133 (Thomas et al. 2007).
The amount of lithium required to suppress expansion
depends on the form of lithium, the nature of the reactive
aggregate, and the amount of alkali in the concrete. Many
studies have shown that the expansion of concrete for a
given aggregate depends on the amount of lithium relative
to the amount of sodium plus potassium in the mortar or
concrete mixture.
Numerous structures have been treated by spraying the
surface of the structure with a solution of lithium (both
LiNO3 and LiOH have been used). Very little lithium penetrates below 1 to 2 in. (25 to 50 mm) unless the concrete
is heavily cracked. Even in heavily cracked concrete, the
lithium concentration decreases with depth, and its ability to
suppress ASR is questionable.
Electrochemical impregnation techniques have been used
to increase lithium penetration on a number of structures.
Significant lithium can penetrate to a depth of at least 0.75 to
1.25 in. (19 to 32 mm), and these dosages are theoretically
high enough to have a beneficial effect on reducing ASRinduced expansion.
Vacuum impregnation is an alternative to pressure injection and has been used to increase grout penetration into
cracked concrete. A number of structures have been treated
with lithium using this technique; however, documentation
of the benefits is not sufficient to draw reliable conclusions.
Before treating a structure with lithium-based compounds,
an investigation should be conducted to ensure that the
primary cause of damage is ASR. Lithium treatment is
unlikely to cure any other deterioration processes such as
freezing-and-thawing damage, corrosion of embedded steel,
or even alkali-carbonate reaction (ACR). Proper diagnosis
involves extracting samples for petrographic analysis and
other testing in the laboratory. Following treatment, the
potential for further expansion and damage due to ASR can
still remain.
Lithium treatment will not repair any damage that has
already occurred. A protocol for selecting structures that
may be suitable for lithium treatment is available from the
Federal Highway Administration (FHWA) HRT-04-113
(Thomas et al. 2004) and FHWA recommendations for
lithium to mitigate ASR.
Treating structures with lithium is a technology that is
still under development, and recommended protocols for
selecting the type of treatment (for example, topical, electrochemical, or vacuum impregnation) or methodologies for
performing the treatment do not exist. Electrochemical and
vacuum impregnation requires specialized knowledge and
equipment, and should be conducted only by an experienced
contractor
4.2.9.6 Anti-washout admixtures—Anti-washout admixtures (AWAs) are chemical admixtures that bind the free
water in the concrete mixture and reduce the loss of fine
materials from the concrete mixture into the water during
placement of concrete under water.
4.2.9.6.1 Advantages—Anti-washout admixtures are often
used in concrete mixtures proportioned for underwater
placement. The AWA improves the flow and cohesion characteristics of the mixture. The loss of cement and other fine
material from the mixture due to contact with water during
placement is reduced, thus improving the in-place concrete
properties. The mixtures can be proportioned to be selfconsolidating and to flow around reinforcement.
4.2.9.6.2 Limitations—Concretes made with AWAs are
often tacky, may exhibit long setting times, and are sensitive to slight changes in the w/cm and admixtures. Concretes
made with AWAs typically are rich in cementitious materials and may therefore require evaluation of thermal
stresses when used in large placements. High-range waterreducing admixtures are used to maximize the benefit of the
AWA. Compatibility of admixtures, particularly when airentraining admixtures are used, should be evaluated using
trial batches.
4.2.9.6.3 Applications—Concretes using AWAs are used
for underwater concrete placement. The mixtures can be
placed by tremie, pump, or slipform. Applications include
concrete repair as well as new construction. Anti-washout
admixtures may allow free fall of concrete mixtures through
2 to 3 ft (0.6 to 0.9 m) of water during placement. Concrete
made with AWA is less susceptible to loss of material due to
contact with slowly flowing water.
4.2.9.6.4 Standards—Anti-washout admixtures should
conform to USACE specification CRD-C 661 (USACE
2006). Test method CRD-C 61 (USACE 1989) can be used
to measure the loss of cement paste/fines from freshly mixed
concrete resulting from contact with water.
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
4.2.10 Other concrete and mortar additives—Materials
added to concrete and mortar that are not supplementary
cementitious materials and do not fall under the definition of
an admixture are contained in this section.
4.2.10.1 Fiber reinforcement—Fiber reinforcement
consists of conventional concrete reinforced with discrete
reinforcing fibers. ACI 544.1R identifies four classifications
of fiber-reinforced concrete (FRC): steel fiber-reinforced
concrete (SFRC); glass fiber-reinforced concrete (GFRC);
synthetic fiber-reinforced concrete (SNFRC); and natural
fiber-reinforced concrete (NFRC).
Fiber reinforcement of building materials such as brick
and adobe has been practiced for thousands of years. Reinforcing concrete with fibers has become an accepted design
option where crack control due to plastic, drying, or servicerelated shrinkage is desired. Fiber-reinforced concrete has
been shown to provide significant increases in durability
and impact resistance. Using polyolefin fibers to improve
the spalling resistance of concrete in fire events by allowing
steam ventilation is well documented. Research has developed promising results in various structural applications
such as steel-deck-formed slabs, structural slabs-on-ground,
and formed elevated concrete slabs. Using fibers in combination with conventional reinforcing steel is practiced where
both structural strength and improved crack resistance are
needed.
Fiber-reinforced concrete has been successfully used for
concrete repairs using conventional and shotcrete placement.
Though all four types of fibers have been used to produce
FRC, SFRC and SNFRC are more applicable to the concrete
repair industry, while GFRC and NFRC are more applicable
to the fabricated building products industry. Information on
fiber-reinforced concrete or shotcrete can be obtained from
ACI 544.1R, ACI 544.3R, ACI 544.4R, and ACI 506.1R.
4.2.10.1.1 Advantages—Fibers are typically added during
concrete production whether plant- or site-mixed. These
fibers can be used to provide reinforcement in thin overlays
where installation of conventional reinforcing bars is impractical. The addition of fibers can also increase durability and
reduce plastic shrinkage cracking of repair materials. Areas
subject to shock or vibration loading, where plastic shrinkage
cracking is a problem or where blast resistance is required,
can benefit from the addition of fiber reinforcement.
4.2.10.1.2 Limitations—The addition of fibers reduces
the slump and can cause workability problems for inexperienced workers. Rust stains may occur at the surface of SFRC
due to corrosion of fibers at the surface.
4.2.10.1.3 Applications—Fiber-reinforced concrete has
been used for slabs-on-ground, overlays of concrete pavements, slope stabilization, and reinforcement of structures
such as arches or domes. Reinforced concrete structures
have been repaired with fiber-reinforced shotcrete. Research
has found potential structural applications for FRC in new
construction. Advances in the use of FRC may provide
future applications in the repair industry.
4.2.10.1.4 Standards—ASTM C1116 covers the materials,
proportions, batching, delivery, and testing of fiber-reinforced concrete and shotcrete.
27
4.2.11 Combination materials—The preceding repair
materials are often used in combination to enhance important properties for specific applications. As an example,
rapid-setting cement is used instead of conventional Type
I/II to produce very-high-early-strength polymer-cement
concrete. Whereas conventional LMC overlays should be
cured 4 to 7 days before being opened to traffic, high-earlystrength LMC (LMC-HE or LMC-VE) can be subjected
to traffic in less than 1 day. Using LMC-VE reduces down
time and inconvenience to motorists; allows for installation at night; provides negligible to very low permeability;
and produces high strength, particularly high early strength
(Sprinkel 1998).
4.3—Crack repair materials
4.3.1 Epoxy resin—Epoxy resin is a thermosetting polymer
that cures when mixed with a catalyzing agent or hardener.
Epoxies have been the products of choice for crack repair in
the industry for decades. Once cured, epoxies have exceptional physical properties. Epoxies are recognized for their
superior bond strength to concrete, which typically exceeds
the tensile strength of normal concrete. Commercially available epoxies have been formulated to meet variable working
time requirements and offer a wide range of viscosities.
4.3.1.1 Advantages—There is no special surface preparation required to the inside of the crack that is being repaired.
If the crack is wide enough, debris can be vacuumed out
of the crack Cracks repaired with epoxies are considered
structural repairs. Low-viscosity epoxies have been proven
to repair cracks as thin as 0.002 in. (0.05 mm) wide. Some
commercially available epoxies can develop bond in damp
concrete cracks.
4.3.1.2 Limitations—Epoxies are used to repair cracks that
typically range from 0.002 to 0.25 in. (0.05 to 6 mm) wide.
Because the coefficient of thermal expansion of the epoxy
resin and the concrete are vastly different, a thicker cross
section of the epoxy in a crack exposed to large temperature
variations can cause internal stresses in the repaired concrete.
Epoxy resin should only be used in nonmoving or dormant
cracks. Cracks that continue to move after they have been
repaired with an epoxy are likely to develop cracks parallel
to the original cracks. Also, some epoxies used for crack
injection may be sensitive to the moisture saturation in the
crack. Mixing epoxy in proper proportions is critical to the
performance of the product. Epoxy resins that are incorrectly mixed result in improperly cured material
4.3.1.3 Application—Epoxies are injected into cracks
using multiple methods and techniques such as gravity feed
and pressure injection. Properties of the chosen material
should be considered when selecting the appropriate application method. In-depth application method descriptions
can be found in 5.2.1. Refer to ACI 546.3R, ACI RAP-1,
and Trout (2006) for additional information on crack repair
materials and typical applications.
4.3.1.4 Standards—ASTM C881 classifies epoxies by
their intended use, viscosity, and temperature limitations.
The standard classifies seven different types of epoxies.
Injection resins are generally classified as Type 1, non-
American Concrete Institute – Copyrighted © Material – www.concrete.org
28
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
load-bearing applications for bonding hardened concrete to
hardened concrete or Type IV, load-bearing applications for
bonding hardened concrete to hardened concrete.
4.3.2 Urethane resins—Urethane resins, such as epoxy
resins, are thermosetting polymers. Many moisture cure,
while some cure when mixed with a catalyzing agent or hardener. They have been formulated as rigid and flexible products with a range of working times, allowing for application
in a wide array of repair conditions. They are also available
in different viscosities, some ranging to below 9 cP (1.31
× 10-6 lb·s/in.2 [0.009N∙s/m2]) with surface tensions below
0.0021 lb/ft (0.03 N/m) to allow penetration of the substrate
for structural repairs. Some products may also be applied
with the addition of aggregate to accommodate larger repair
areas. As with cement-based repair products, urethane resins
with similar strength to existing concrete should be selected
for structural repairs.
4.3.2.1 Advantages—Urethane-based repair materials
are recognized for their rapid curing. Some fully cure in 10
minutes at 70°F (21°C). Additionally, they are recognized
for their ability to penetrate and structurally repair concrete
and their suitability in a wide range of repair applications.
They are available for the repair of moving and static cracks
of varied widths and depths. In addition, urethane products
are available that can be applied at temperatures below
–20°F (–23°C). Unlike epoxy resins, which often have
higher compressive strengths, urethane resins are available
with compressive strengths in the 4000 to 5000 psi (27.5 to
34.5 MPa) range, similar to typical concrete substrates.
4.3.2.2 Limitations—Urethane resins may be sensitive to
moisture before curing, requiring surrounding concrete to
be dry and cured for at least 60 days at time of application.
Urethane resins may also be sensitive to UV rays, causing
them to yellow in appearance over time when exposed to
UV sunlight. When low-viscosity, low-surface-tension products are used, such resins may leak out of full-depth repairs.
Typically, the full-depth repair area is first filled with dry
sand and then the urethane is poured in. A second application
may be needed after the first has cured.
4.3.2.3 Applications—Urethane resins are typically
gravity-injected to achieve full- or partial-depth repairs,
depending on application. When applying low-viscosity,
low-surface-tension products, specified aggregates may be
added to the repair to reduce penetration of material for
partial-depth repairs. For full structural repairs, material
should be allowed to gravity feed the full depth of the repair
area. Once this has been achieved, sand may be introduced
to prevent under-slab ponding and waste. The addition of
sand also adds strength to the repair and brings the thermal
coefficient of expansion of the repair material closer to that
of the surrounding concrete.
4.3.3 Polyurethane chemical grouts—Although there
are other forms of chemical grouts, polyurethanes are the
most common choice of material for repair of cracks by
chemical grouting, and are classified into hydrophobic and
hydrophilic types. Polyurethane chemical grouts consist of a
polyurethane resin that reacts with water to form an expansive, closed-cell foam or a gel. Hydrophobic types are gener-
ally recommended for applications subject to intermittent
wetting and drying; hydrophilic types should be continuously wet (USACE 1995b). Refer to ICRI 340.1 for additional information.
4.3.3.1 Advantages—Polyurethane chemical grouts are
typically used to repair both wet and active cracks, or cracks
leaking a significant amount of water. Some grouts are
semi-flexible; thus, they may tolerate some change in crack
width. Therefore, understanding crack movement is a key
consideration in selecting a polyurethane chemical grout.
The reaction time to form the foam may be controlled from
a few seconds up to several minutes using different catalyst
additives. For example, where a crack is leaking heavily, the
polyurethane chemical grout reaction may be highly accelerated to stop the leak. These grouts penetrate effectively, and
the technique of chemical grouting is a well-proven method
of repairing cracks.
4.3.3.2 Limitations—Polyurethane chemical grouts generally are not suitable for structural repairs. Additionally,
a highly skilled work crew is required along with special
injection equipment. Finally, these materials typically are
not stable when exposed to UV light. This is typically not a
major concern because the material is injected into a narrow
crack, where exposure to UV light is minimal.
4.3.3.3 Applications—Polyurethane chemical grouts may
be used to treat cracks 0.005 in. (0.12 mm) and greater in
width and are injected at high pressures. Polyurethane grouts
are suitable for injection of vertical, overhead, and horizontal
cracks that are active or leaking. Their ability to stop active
leaks makes them particularly well-suited for liquid storage
tanks, dams, tunnels, sewers, and other water-containment
structures.
4.3.3.4 Standards—No standards exist for polyurethane
chemical grouts. ASTM D1623 may be used to determine
the tensile strength and elongation properties of the grout at
all urethane-to-water ratios.
4.3.4 Polyurethane sealant—Polyurethane sealants, also
known as urethane sealants, are based on polymers that result
from the reaction of an isocyanate and a hydroxyl-bearing
compound, such as a polyol. Polyurethane polymers are
typically blended with fillers, colorants, curing agents, and
other additives that govern viscosity, adhesion, long-term
stability, and resistance to weathering. Polyurethane sealants
are formulated for treating both static and dynamic (moving)
cracks, filling concrete and masonry joints. Product formulations are tailored for use in horizontal or vertical surfaces, as
well as exposure to continuous water immersion.
4.3.4.1 Advantages—The advantages of polyurethane
sealants include their overall adhesion to unprimed concrete
and other porous surfaces. Once tested and verified, they
provide virtually unlimited color selection (especially in
multi-component materials); they have an ability to be used
in cracks and joints (as wide as 2 in. [50 mm] in some cases);
and they have extremely low incidence of surface or migratory staining when applied against concrete, masonry, and
other porous materials. Some polyurethanes are formulated
for environments requiring enhanced physical durability
such as pedestrian or vehicular traffic surfaces. Polyurethane
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
sealants are also frequently used in combination with deck
coatings or architectural wall coatings, with which they must
be chemically compatible for both materials to function
properly. The movement capability of most polyurethanes
enables them to accommodate normal dimensional changes
in concrete due to structural and thermal stresses.
4.3.4.2 Limitations—Single-component polyurethanes
require the presence of atmospheric moisture to cross-link
and develop their design properties. In arid environments
or cool, dry weather conditions when atmospheric moisture is scarce, such a sealant may be damaged by repeated
movement cycles or traffic exposure before it can substantially cure. Single-component materials also typically have
a limited color palette from which to choose. Multiplecomponent sealants, on the other hand, require careful and
thorough mixing to develop their intended properties after
installation.
4.3.4.3 Applications—Polyurethane sealants are used in
the repair of static or dynamic cracks and joints in vertical
elements—for example, wall panels or horizontal surfaces
such as pedestrian and vehicular traffic areas. Specialty
applications include water-immersion situations such as
tanks, dams, and reservoirs, and security work such as joints
in window perimeters in detention facilities, which require a
harder, tamper-evident material.
A good joint design is critical to ensure that the sealant
material performs properly; therefore, a 2:1 joint width-todepth ratio should be maintained. Some smaller cracks will
have to be routed to comply with these limitations.
4.3.4.4 Standards—ASTM C920 governs virtually all
applications where polyurethane sealants are used. Historically, Federal Specifications, such as TT-S-00230C for
single-component sealants and TT-S-00227E for multiplecomponent sealants, have also been used. Although these
specifications are still frequently cited, they are no longer
maintained, and their use has been superseded by ASTM
C920.
4.3.5 Silicone sealant—Silicone sealants are based on
polymers where the polymer backbone consists of alternating silicon and oxygen atoms with carbon-containing side
groups. These sealants have different curing mechanisms,
depending on the end group of the polymer. Typically, silicone sealants contain silicone polymers, fumed silica, plasticizers, calcium carbonate fillers, and silanes for adhesion.
4.3.5.1 Advantages—Silicone sealants are highly resistant
to UV light and do not chalk or change color even when
exposed for long periods of time. Silicone sealants have high
elongation properties (1000 percent and greater per ASTM
D412), making them suitable for active joints.
4.3.5.2 Limitations—Silicone’s adhesion to concrete and
masonry can be inadequate unless a primer is used. Silicone
sealants should not be used for immersion; thus, they are not
used for sealing joints within water tanks, reservoirs, dams,
and similar applications. Additionally, silicones may only be
overcoated with silicone-based coatings.
Oils within the silicone sealants will often migrate into a
porous substrate, resulting in staining of the substrate, making
these materials aesthetically unacceptable. Nonbleeding sili-
29
cones are commercially available to address this specific
issue.
4.3.5.3 Applications—Silicone sealants are generally used
to seal cracks that range from 0.1 to 2 in. (2.5 to 50 mm) in
width. Joint widths should range from 0.25 to 1 in. (6 to 25
mm) and depths should range from 0.25 to 0.5 in. (6 to 13
mm). These products are suitable for vertical and overhead
applications. Some manufacturers offer sealant formulations suitable for traffic. Silicone sealants are not suitable for
structural repairs.
A good joint design is critical to ensure that the sealant
material performs properly; therefore, a 2:1 joint widthdepth ratio should be maintained. Some smaller cracks will
have to be routed to comply with these limitations.
4.3.5.4 Standards—ASTM C920 governs virtually all
applications where silicone sealants are used. Historically,
Federal Specifications, such as TT-S001543A for singlecomponent silicone sealants, have also been used. The
Federal Specifications, although still frequently cited, are
no longer maintained, and their use has been superseded by
ASTM C920.
4.3.6 Methacrylates—Methacrylates are liquid resins
used to seal concrete slabs and structurally heal small,
shallow cracks wider than 0.005 in. (0.12 mm). Because of
their high adhesive strength, methacrylates can bond cracks
as a structural repair. The most common types are HMWM
and reactive methacrylates. Both types are similar in application and performance to super-low-viscosity epoxies, with
the viscosity of methacrylate resin typically below approximately 30 cP (4.35 × 10–6 lb·s/in.2 [0.03 N·s/m2]).
4.3.6.1 Advantages—Although methacrylates are generally considered semi-rigid and not appropriate for resisting
structural movement, cracks bonded using methacrylates
can typically resist movements caused by traffic vibration.
Flood-coating a concrete slab using methacrylates will fill
and bond small cracks, such as shrinkage cracks, and seal
the slab against the penetration of water, salts, or other deleterious chemicals. Methacrylates also perform well at cold
temperatures and even achieve good bond to cured and aged
methacrylate so recoating is possible, unlike epoxies.
4.3.6.2 Limitations—Because methacrylates are typically installed using flood-coat techniques, ensuring a fulldepth structural repair can be difficult. Because of their low
viscosity, methacrylates are rarely pressure injected. Methacrylates can leak out of full-depth cracks because they have
such low viscosity and surface tension. Typically, the fulldepth crack is first filled with dry sand and then the methacrylate is poured in. A second application may be needed
after the first has cured. If a full-depth repair of larger cracks
is needed, pressure injection using epoxies should be considered instead. Methacrylates are best applied to horizontal
concrete surfaces, although they can be used on sloped
concrete surfaces such as parking garage entry ramps.
However, because of the very low viscosity of the materials,
care should be taken on sloping surfaces to prevent the material from flowing out of cracks. Although methacrylates are
commonly seeded with aggregates, the effect of the methacrylate on skid resistance should be considered for bridge
American Concrete Institute – Copyrighted © Material – www.concrete.org
30
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
decks exposed to heavy traffic and high speeds. Some methacrylates, particularly reactive methacrylates, can have a
strong odor. Protection should be provided to keep the work
area away from direct contact with the public, especially in
enclosed areas or in close proximity to building air intake
vents. Three-component HMWM formulations should be
mixed with extreme care, as they can react violently if mixed
improperly. The promoter should be mixed thoroughly into
the resin before adding the catalyst. Never mix the catalyst
and promoter directly together.
4.3.6.3 Applications—Flood-coating with methacrylates
is well suited to bridge decks, parking garages, and industrial floors or other concrete slabs that have a large number
of random cracks but no evidence of steel corrosion or
alkali-aggregate reaction. Before installation, care should be
taken to ensure the cracks are open, clean, and free of any
contaminants or other bond-inhibiting materials such as oil
and grease. Because methacrylates can be sensitive to moisture, the substrate should be dry at the time of application.
For more information on proper application procedures,
refer to RAP-13.
4.3.6.4 Standards—There is no standard specification for
methacrylates; however, RAP-13 may be referenced. Similar
to epoxies, ASTM C882 can be used for evaluating the bond
strength of methacrylates.
4.3.7 Polymer grout—Polymer grout is a mixture where
a polymer, such as an epoxy resin, serves as the binder.
Sand—typically oven-dried silica with a grading from No.
20 to +40 mesh (0.8 to 0.4 mm)—is generally mixed as the
filler. Depending on how much resin is added, the variability
of the polymer grout can be adjusted from a stiff material
suitable for hand-packing large cracks on overhead and
vertical surfaces or to a pourable consistency grout suitable
for gravity-feeding cracks in horizontal slabs.
4.3.7.1 Advantages—Polymer grouts bond extremely well
to concrete and have low shrinkage, resulting in a liquid-tight
repair in dormant cracks. Similar to epoxy resins, polymer
grouts are suitable for cracks requiring structural repairs.
Because of their rigidity, if polymer grouts are used in cracks
that experience movement, parallel cracks may appear adjacent to the repaired cracks. Materials of varying consistencies are readily available to repair cracks in vertical, overhead, and horizontal applications. Whereas a few polymer
grouts may effectively bond to concrete with some moisture
present in the concrete pores, most polymer grouts marketed
for construction will not bond to concrete in the presence of
moisture. The chemical resistance of polymer grout is generally much better than that of normal concrete. Finally, these
materials may be designed for a fast cure to minimize the
downtime due to repairs.
4.3.7.2 Limitations—As with epoxy resins, it is critical
to properly proportion the resin and the hardener and to
thoroughly mix the sand to get the desired polymer grout.
Failure to do so could result in a grout that never cures or
cures incompletely. Generally, the temperature exposure
of these materials should not exceed 120 to 250°F (49 to
66°C). The first detectable loss of strength could occur at
these temperatures.
4.3.7.3 Application—Polymer grout is typically used to
repair dormant cracks 0.25 in. (6 mm) and greater in width.
Polymer grouts can be hand-applied and packed into large
cracks regardless of orientation, or they can be poured into
cracks located within horizontal slabs. No special equipment, except the personal protective equipment required for
handling the material, is required to apply these materials.
The required applicator skill levels are low to moderate. To
produce a polymer grout, the resin and hardener are mixed,
and then the filler is gradually added while mixing until a
homogenous mixture is achieved. Mixing is typically done
with an eggbeater-style mixing blade and a hand-held electric drill. Pot life or working time may be varied to suit the
application. Long pot-life products enable the applicator to
mix and apply larger quantities. Fast-cure products allow
rapid turnovers; however, care should be taken to mix only
sufficient material that may be applied within the specified
pot life.
4.3.7.4 Standards—No standards exist for polymer grouts
intended for use as crack repair. ASTM C882, D638, and
D695 should be considered when evaluating these materials. ASTM C881 classifies epoxies by their intended use,
viscosity, and temperature limitations.
4.3.8 Polymer-cement grout—Polymer-cement grout is
a mixture consisting primarily of cement, fine aggregate,
water, and a polymer such as acrylic, styrene-acrylic, styrenebutadiene, or a water-borne epoxy. The consistency of this
material can be adjusted from a stiff material suitable for
hand-packing large cracks on overhead and vertical surfaces
to a pourable consistency suitable for gravity-feeding cracks
in horizontal slabs.
These materials are available in a wide range of consistencies suitable for applications requiring improved physical
properties including bond strength, compressive strength,
and flexural strength as compared with conventional waterbased cement grouts that do not use polymers.
4.3.8.1 Advantages—No special tools and equipment
are necessary except the required personal protective
equipment; the required applicator skill levels are low to
moderate. These materials are generally more economical
than polymer grouts.
4.3.8.2 Limitations—The potentially high shrinkage of
polymer-cement grouts compared with polymer grouts may
make it difficult to obtain a watertight repair. Additionally,
these materials are not as chemically resistant as the polymer
grouts.
4.3.8.3 Applications—Polymer-cement grout is generally
used to repair cracks 0.25 in. (6 mm) and greater in width.
The surface should be prepared to ensure a clean, open-pore
substrate. The substrate should be in a saturated surface-dry
(SSD) condition, with no standing water at the time of application. Mixing should be done using a drill and paddle or an
appropriate mixer. The material should be scrubbed into the
substrate to fill all pores and voids, and then packed into the
crack and finished flush with the concrete surface.
4.3.8.4 Standards—The polymer component should
conform to the requirements of ASTM C1438, Type II. No
standards exist for mixtures of the polymer component with
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
grout; however, recommended tests for these materials are
found in ASTM C1439, C157, C293, C469, C496, and C531.
4.3.9 Cement grout—Cement grout is a mixture of
cementitious material and water, with or without admixtures, aggregates, or both, that is proportioned to produce
consistencies ranging from pourable to stiff. Admixtures are
often used in an attempt to eliminate segregation of constituents in pourable applications.
Cement grouts mixed with fine aggregate typically have
mixture ratios that vary from 2:1 sand-to-cement proportions, to grouts that are neat cement without sand, measurements are parts by volume. When filling a crack with grout,
the crack width should be wide enough for the grout to fill
the crack and also penetrate the crack depth. For this reason,
the fine aggregate size can be the limiting factor for proper
crack fill of tight cracks. Cracks smaller than the sand-aggregate diameter should be filled with neat cement grout.
The consistency of the grout may vary from a stiff material suitable for hand-packing large cracks on overhead
and vertical surfaces to a pourable consistency suitable for
gravity feeding cracks in horizontal slabs. The amount of
water added controls the grout consistency.
4.3.9.1 Advantages—No special tools or equipment are
necessary and the required applicator skill levels are low
to moderate. Cement grout is typically the least expensive
repair grout because there are no additional binders other
than the cement.
4.3.9.2 Limitations—Cement grouts can be used for
repairs by injection, but only where the width of the opening
is sufficient to accept the solid particles suspended in the
grout. The minimum crack width at the point of introduction
should be approximately 0.25 in. (6 mm).
4.3.9.3 Applications—Cement grout is generally used to
repair cracks 0.25 in. (6 mm) and greater in width. For additional applications, refer to 4.2.4.3. The substrate should be
clean, sound, and damp at the time of application. The material should be packed into the crack and finished flush with
the concrete surface.
4.3.9.4 Standards—There are no standards developed
strictly for grouts to repair cracks. ASTM C1107 is intended
for materials used under applied loads such as base plates for
a structure or machine.
4.4—Bonding materials
Bonding materials can be used to bond new repair material
or fresh concrete to an existing prepared concrete substrate.
Based on the chemistry, bonding materials can be classified as one of four types: 1) epoxy-based; 2) latex-based; 3)
modified epoxy-based; and 4) cement-based.
4.4.1 Epoxy bonding materials
4.4.1.1 Advantages—Epoxy resins have been widely and
successfully used in the industry as a bonding agent for many
years. Epoxy bonding agents are known for their excellent
adhesive properties. Over the years, improvements to the
chemistry have allowed epoxy agents to be moisture tolerant.
Epoxy bonding agents perform best when the substrate is
dry and when prewetting the surface is impractical. It is to
be expected that when an epoxy is used as a bonding agent,
31
the bond strength at the bond line should exceed the tensile
strength of the substrate and repair concrete.
Epoxies can have very high compressive and bond
strength while maintaining good flexural properties. Their
adhesion to substrates, especially imperfect surfaces, makes
them useful in many applications. Epoxies commonly have
a high shore hardness and can withstand abuse from weather
and abrasion. If an epoxy is made up of 100 percent solids,
the shrinkage values are very low. Once an epoxy is cured,
its chemical resistance is very high, which makes epoxies a
good choice for volatile environments. Epoxy can be formulated to cure at varying rates; thus, an epoxy can be chosen
to fit the project-specific criteria.
4.4.1.2 Limitations—Care should be taken when using
these materials at all times, especially in hot weather, as high
temperatures may cause premature curing and creation of
a bond breaker. Most epoxy-resin bonding materials create
a moisture barrier between the existing substrate and the
repair material. Under certain conditions, such as slabs-onground in a freezing-and-thawing environment, a moisture
barrier could result in failure of the repair when moisture
becomes trapped beneath the moisture barrier and freezes.
In such cases, epoxy resins should not be used for slab-onground concrete overlays. If epoxy resins are used in such
situations, applying the epoxy intermittently over the area
(leaving areas without an epoxy barrier) may provide satisfactory results.
4.4.1.3 Applications—Surface preparation is critical for
proper epoxy performance. The surface should be clean
and sound. It may be slightly damp but should be free of
standing water. Dust, laitance, grease, curing compounds,
impregnations, waxes, and any other contaminants should
be removed before placing the epoxy resin. Concrete should
have an open-textured surface prepared by blast cleaning or
other equivalent mechanical methods. Steel should be blast
cleaned to a white metal finish.
Two-component epoxy bonding agents are mixed mechanically to obtain a uniform mixture. Once mixed, epoxy is
typically applied with a brush or roller. Larger jobs may
use approved spraying equipment for a faster production
rate. Proper protective gear as suggested by the manufacturer should be used in working with epoxy resins. Clean-up
of the epoxy material should be performed with approved
chemicals. Epoxy can bond fresh or hardened concrete to
metal, wood, or concrete.
4.4.1.4 Standards—Epoxy systems are covered in ASTM
C881 and AASHTO M-235 specifications. ASTM C881
categorizes epoxy resins by “type” (application characteristics), “grade” (viscosity), “class” (reaction rate), and color,
which define their intended use.
4.4.2 Latex bonding materials
4.4.2.1 Advantages—Latex-based bonding agents are
more economical in comparison to an epoxy or modified
epoxy bonding agent, and are easier to handle on job sites.
Clean-up of latex-based bonding agents is relatively easy
before drying, but is more difficult after drying. Their very
low viscosity results in relatively easy application. Latex
bonding agents are classified as Type I or II per ASTM
American Concrete Institute – Copyrighted © Material – www.concrete.org
32
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
C1059. Type I bonding agents can be applied to the bonding
surface several days before placing the repair materials. Type
II bonding agents are best suited for bonding when mixed
with cement and water to produce a slurry. These are most
commonly used with polymer-modified concrete mixtures.
4.4.2.2 Limitations—The bond strength of latex-based
bonding agents is substantially less than that provided by
epoxy-based bonding agents. Type I bonding agents should
not be used in areas subject to water, high humidity, or structural applications. Leaving the concrete surface primed for
an extended period of time can potentially contaminate the
surface.
Type II bonding agents act as bond breakers once they
have skimmed over or cured. Many manufacturers recommend Type II admixtures to be used as an additive in the
concrete or mortar mixture to promote bond in place of a
film-forming bonding bridge.
4.4.2.3 Applications—Latex bonding agents are applied
with a brush, roller, or broom.
4.4.2.4 Standards—Latex systems are covered in ASTM
C1059. Latex bonding agents are classified as Type I—
Redispersible, and Type II—Nonredispersible.
4.4.3 Modified epoxy bonding materials
4.4.3.1 Advantages—Modified epoxy-cement bonding
agents have been successfully used in the repair industry
for many years. Commercial products classified as modified epoxy bonding agents are typically three-component
products. In addition to the two-component resin, the third
component in these systems is cement-based. These products
are practical for spall-repair applications. Unlike neat epoxy
resins, these products allow longer open working time for
placement of material or concrete. The open times depend
on temperatures. These bonding agents do not create a bondinhibiting surface and recoating is possible if open times to
place concrete or a repair material are exceeded. Manufacturers’ recommendations should be followed to understand
and work within the limitations of the product.
4.4.3.2 Limitations—Due to the slurry consistency of
modified epoxy bonding agents, care should be taken to
ensure appropriate mill thickness is achieved on the concrete.
4.4.3.3 Applications—Stiff brush is the most common
method for limited size areas. Spray equipment can also be
used to apply the material for larger areas. Modified epoxy
bonding agents use water-based epoxy, so clean-up is easy
with water, provided the material has not hardened.
4.4.3.4 Standards—There are no known industry standards that govern modified epoxy cement bonding agents.
ASTM C882 has been used to test modified epoxy cements.
4.4.4 Cement-based bonding materials
4.4.4.1 Advantages—Cement-based systems have been
successfully used for many years. Cement bonding systems
use neat portland cement or a blend of portland cement and
fine aggregate filler proportioned 1-to-1 by mass. Water is
added to provide a uniformly creamy consistency. Cementitious slurries are commonly used with PCC.
4.4.4.2 Limitations—Cement-based slurries dry quickly
and can cause bond problems if allowed to dry prematurely.
The skill and experience of the applicator is critical to
achieving proper performance. Where applicators provide a
more flowable mixture for ease of application, the resultant
higher w/cm may result in weaker material at the bond line.
4.4.4.3 Applications—Stiff-bristled brush is commonly
used to apply the material.
4.4.4.4 Standards—There are no known standards that
govern the use of cement-based slurries as a bonding agent.
4.5—Coatings on reinforcement
Some coatings applied to steel reinforcing bars have been
proven to slow the rate of corrosion in laboratory environments and in the field (Popovic 1998). Commonly used coatings include epoxy, zinc, cementitious, latex cement, acrylic
latex, or a combination of these materials.
4.5.1 Advantages—Coatings act as a barrier to prevent
the steel from being exposed to air, water, or other corrosive chemicals. Because the steel is susceptible to corroding
when exposed to air and water, the coating protects the steel
from these elements. Additives are often used within coatings to further reduce or inhibit corrosion.
4.5.2 Limitations—The performance capability of coatings have been challenged due to holidays in the coating
when field applied. The thickness of the coating applied can
affect performance. In addition, once proprietary coatings
are applied, corrosion activity can no longer be determined
by standard testing procedures.
A thorough literature search of these materials and consultation with the manufacturer should be conducted before
using these materials.
4.5.3 Applications—Coatings are typically applied to
exposed reinforcing steel in concrete repairs. Exposed reinforcing steel bars should be dry and thoroughly cleaned,
often by abrasive blasting, to remove all rust and concrete
before installing a coating. Coating should be applied
uniformly and fully encapsulate the reinforcing bar.
4.6—Reinforcement
Structural concrete members typically require reinforcement when subject to tensile stresses due to flexure, shear,
and axial loads. When the repair design requires reinforcement, several options are available, including various corrosion-resistant materials and conventional uncoated reinforcing steel.
4.6.1 Uncoated steel reinforcement—ACI 318 specifies steel reinforcement as deformed bars, spiral bars, and
welded-wire reinforcement, with grades conforming to
ASTM A615, A616, A617, or A706 for bars; ASTM A185
for plain wire reinforcement; and ASTM A497 for deformed
wire reinforcement.
ACI 301 and 318 further specify minimum concrete
cover requirements for various environmental exposures,
maximum levels of chlorides, recommended w/cm of
concrete mixtures, and other guidelines to improve concrete
performance, all of which contribute to minimizing the
potential for corrosion of conventional reinforcing structural
elements.
4.6.2 Fusion-bonded epoxy-coated steel reinforcement—
Epoxy coatings on conventional reinforcing steel (ASTM
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
A775) were introduced in the mid-1970s to act as a barrier
to the elements that initiate corrosion, including oxygen,
moisture, and chlorides. Though shown to be an effective
method of reducing steel corrosion in concrete bridge decks,
in-service performance of epoxy-coating varies depending
on the moisture content of the concrete, the quality of the
coating, damage to the coating during installation, extent
of concrete cracking, depth of cover, loss of adhesion
between coating and reinforcement, and level of chloride
concentrations.
4.6.3 Galvanized reinforcement—Hot-dipped galvanized
reinforcing steel is also available as a method for reducing
corrosion in reinforced concrete. ASTM A767 specifies
the requirements for zinc-coated (galvanized) reinforcing
bars, with repair procedures identified by ASTM A780. The
galvanizing process is based on the zinc coating providing a
sacrificial corrosion layer around the reinforcing steel bars.
At field cuts or damaged galvanization areas, application of
zinc paint should be used to coat unprotected steel.
4.6.4 Stainless steel reinforcement—Solid stainless steel
reinforcement is very resistant to corrosion in concrete, with
Grades 304 and 316 being the most commonly used. Grade
316, however, is reported to be more resistant to corrosion
in chloride environments. Stainless steel reinforcement can
also be field bent or fabricated and is resistant to surface
damage during handling and concrete placement. Initial cost
is the primary disadvantage restricting its use, but life cycle
cost analyses can indicate stainless reinforcement to be more
economical over the long term.
4.6.5 Stainless-steel-clad reinforcement—Stainless-steelclad reinforcement offers similar advantages to those of solid
stainless steel bars, but at reduced costs. Field fabrication,
including cutting, bending, and welding, is practical. Repairs
at cut ends, however, are typically specified to be coated.
Stainless-steel-clad reinforcement is not readily available.
4.6.6 Composite nonmetallic reinforcement—Fiber-reinforced polymer (FRP) composites are systems composed of
high-strength fibers and a resin matrix. They generally use an
epoxy resin, although other resin systems exist such as vinyl
esters and polyesters. The typical fibers are carbon, glass, or
aramid, with material properties, durability, and cost varying
for each. FRPs are available in shapes similar to conventional reinforcement and are used for internal reinforcement
(ACI 440.1R) and near-surface mounted (NSM) bars (ACI
440.2R). Fiber-reinforced polymer is also available in flat
bar shapes or sheets to be applied on the external surface of
concrete, generally with epoxy (ACI 440.2R). The following
sections address the use of externally bonded FRP systems.
4.6.6.1 Advantages—FRP systems offer a high strength-toweight ratio, allowing for a simple installation. The systems
can be designed to perform similarly to conventional repair
schemes such as steel plating and shotcreting. FRP materials
are not subject to atmospheric corrosion and are resistant to
chemical environments.
Systems can be installed indoors with little mess and
impact to occupants. Minimal equipment, access, lead time,
and cure time are required for proper performance of FRP
systems.
33
4.6.6.2 Limitations—Temperature and weather can influence the ability to install externally bonded FRP systems.
Extreme temperatures and moisture should be avoided
during the installation of such materials. Typically, in-service
temperature should be below 150°F (66°C); however, some
FRP materials may require lower in-service temperature
limits. These systems should also be protected against UV
exposure and fire.
The successful application of FRP systems depends on the
proven performance of the individual systems, proper design
methodology, environmental protection, and training, skill,
and experience of the installer. Each manufacturer should
demonstrate successful structural tests and material durability of its FRP system, providing the designer with the
necessary data to perform a proper design consistent with
accepted practices and specifying a quality control program
to ensure proper system installation. Due to the inherent
differences within FRP systems, designers should not rely
on the test data of a manufacturer of another system.
4.6.6.3 Applications—FRP systems have been tested
and used for numerous repair and strengthening projects.
Columns, beams, slabs, and walls can be strengthened for
increased seismic performance, additional load capacity, or
damage repair.
FRP-strengthened systems have performed successfully through earthquakes and have generally performed as
designed in field applications. For bonded applications such
as beams, slabs, and walls, the concrete should be sound and
proper surface preparation of the concrete substrate should
follow the guidelines in 3.3.
4.6.6.4 Standards—ICC-ES Acceptance Criteria AC125
defines acceptance criteria for the use of FRP systems,
including validation testing requirements, design methods,
durability tests, and installation quality control. ACI 440.3R
is a guide that covers the determination of material properties for individual material systems and references the
appropriate ASTM test methods developed in the last decade
to characterize FRP for concrete construction.
4.7—Material selection
As described in preceding sections, a wide variety of
conventional and specialty materials are available for
repairing concrete. This large selection provides a greater
opportunity to match material properties with specific
project requirements, but also increases the potential for
selecting an inappropriate material. Bond and compressive
strengths are clearly important material properties for many
repairs, and this information is frequently provided by material suppliers. Some other material properties, however, can
be of equal or greater importance (Warner 1984).
4.7.1 Coefficient of thermal expansion—It is typically
important to use a repair material with a coefficient of
expansion similar to that of the existing concrete. Thermal
compatibility is particularly important in large repairs, overlays, and repairs subjected to wide variations in temperature.
Thermal incompatibility could cause failure either at the
interface or within the lower-strength material.
American Concrete Institute – Copyrighted © Material – www.concrete.org
34
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
4.7.2 Drying shrinkage—Because most repairs are made
on older portland-cement concrete that does not undergo
further shrinkage, the repair material should have minimal
shrinkage to keep from losing bond. Performance criteria for
dimensionally compatible, cement-based repair materials
limit 28-day and ultimate drying shrinkage to 400 and 1000
millionths, respectively (McDonald et al. 2002). Shrinkage
of cementitious repair materials can be reduced by using
mixtures with low w/cm, the maximum practical size and
volume of coarse aggregate, shrinkage-reducing admixtures, shrinkage-compensating concrete providing proper
restraint, or by using construction procedures that minimize
the shrinkage potential. Examples of application procedures
that can be used to minimize the shrinkage of repair materials include dry-pack and preplaced-aggregate concrete.
Shrinkage potential is much greater in thin repairs, such as
1.5 in. (40 mm) or less, when made with cementitious materials. Further, the shrinkage potential is generally believed to
increase as the thickness decreases. Proper curing methods
should be followed.
4.7.3 Permeability—High-quality concrete is relatively
impermeable to liquids, but when moisture evaporates at a
surface, replacement liquid is pulled toward the dry surface
by capillary action. If impermeable materials are used for
large repairs, overlays, or coatings, moisture that rises up
through the base concrete can be trapped between the
concrete and the impermeable repair material. The entrapped
moisture can cause failure at the bond line or critically saturate the base concrete and cause failure by freezing and
thawing if the concrete substrate does not contain a properly
entrained air-void system (USACE 1995a).
4.7.4 Modulus of elasticity—For repaired areas subjected
to loading, the modulus of elasticity of the repair material
should be similar to that of the existing concrete. In nonstructural or protective repairs, a lower-modulus repair material is
desirable to aid in the relaxation of tensile stresses induced
by restrained drying shrinkage.
4.7.5 Chemical properties—Special attention has been
directed in recent years to problems involving corrosion
of embedded reinforcement. In the absence of chlorides or
other corrosive species, a concrete pH within the range of 12
to 14 provides corrosion protection to embedded reinforcement. Repair materials with moderate to low pH values,
however, may provide little, if any, protection to embedded
reinforcement. When such materials are used, because of
constraints including cure time or strength requirements,
additional protection for the existing reinforcement should
be considered. This protection may include techniques such
as cathodic protection or reinforcement coatings. Each
system has its own cost-benefit ratio and should be evaluated for each specific project.
4.7.6 Electrical properties—The resistivity or electrical
stability of a repair material can also affect the performance
of corrosion-damaged concrete following repair. Materials
that have high resistance tend to isolate repaired areas from
adjacent, undamaged areas. Differentials in electrical potential resulting from variations of permeability or chloride
content between the repair material and the original concrete
could increase corrosion activity around the perimeter of the
repair area, resulting in premature failure. This is commonly
called the anodic ring or halo effect. Refer to 3.2.3.1 for
further discussion.
4.7.7 General considerations—The conditions under
which the repair materials are applied and their anticipated
service conditions are critically important considerations in
material selection. Almost every repair project has unique
conditions and special requirements, and only after these
issues have been thoroughly examined can the final repair
criteria be established. Once the criteria are known, often
more than one material can be used with equally good results.
Final selection of the material or combination of materials
should take into consideration the ease of application, cost,
and available labor skills and equipment (Warner 1984). In
areas where failure of a repair could create a safety hazard,
such as repairs on a wall above a public area, the repair
should be designed with adequate mechanical anchorage.
4.7.8 Color and texture properties—For repair of architectural concrete surfaces, color and texture of the repair material should not differ appreciably from the adjacent surface.
Trials should be made on a job-site mockup before beginning actual production work.
CHAPTER 5—CONCRETE AND REINFORCEMENT
REPAIR TECHNIQUES
5.1—Introduction
Various repair techniques are available to restore damaged
and deteriorated concrete and reinforcing steel in structures.
Each repair method has unique advantages, depending on
specific project factors such as physical constraints of the
repair area and costs. The selected repair method can have
a significant influence on the long-term durability of the
concrete repair. This chapter presents the various techniques
for applying the materials presented in Chapter 4 to repair
concrete and reinforcing steel.
5.2—Crack repair
The repair of cracks in concrete is a common concrete
repair procedure, particularly so as a component protection system installation. Cracks can occur in concrete due
to shrinkage, thermal changes, corrosion of embedded
reinforcement, structural-related stresses, and long-term
strain shortening. Only after determining the reason for the
cracking can a proper repair technique be selected.
Structural cracks requiring repair should be able to reestablish load transfer across the crack and restore structural
integrity. Common methods of repair include epoxy injection, gravity feed, and cement grouting. Active cracks,
particularly those caused by thermal changes on exterior
exposures, should be repaired to allow for future movement.
Techniques such as chemical grouting, sealants, and stripand-seal systems have proven effective for repair of active
cracks.
Repairing active cracks on exterior exposures can be difficult. Most of the materials used for crack repair are temperature-sensitive and cannot be installed below 40°F (4°C).
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Active cracks that move due to temperature variations tend
to close in warm weather and open in cold weather. Both the
contractor and the engineer should be aware of this before
selecting the repair method. If feasible, an inspection of the
structure should be conducted in cold weather to document
the location of the cracks requiring repair (ACI 224.1R). It
is also desirable to conduct repairs when the crack is near its
maximum width, because most flexible materials used in the
repair of active cracks perform better in compression than in
tension (Emmons 1993; ACI 504R).
5.2.1 Epoxy injection—Epoxy injection is a crack repair
technique that involves injecting epoxy resin into cracks
under pressure. The injection procedure may vary, subject to
the application and location of the work, as well as size and
accessibility of the cracks. Horizontal, vertical, and overhead cracks (Fig. 5.2.1) require somewhat different injection
approaches. Depending on specific parameters of a project,
crack repair by epoxy injection can restore structural integrity and reduce moisture penetration through cracks as small
as 0.005 in. (0.0.13 mm) in width.
For this method, injection ports are installed along the
crack, and the face of the crack is sealed with an epoxy
paste. Once the epoxy paste has cured, an epoxy resin is
injected into the ports. Typical injection pressures range
from 200 to 300 psi (1400 to 2100 kPa). Higher pressures
of 300 to 500 psi (2100 to 3500 kPa) are commonly used
for fine cracks. Low-pressure injection (15 psi [105 kPa] or
less) is generally used in delicate applications such as architectural surfaces. Using lower pressure permits the use of
easily removable sealants as the capping material. The easy
removal of surface seals allows for maintaining the appearance of the injected surface.
Cracks may be injected from one or both sides of a concrete
member. Where access is limited to only one side, installation procedures may include variations in epoxy viscosities,
injection equipment, injection pressure, and port spacing to
ensure full penetration of epoxy into the cracks. If a crack is
subject to subsequent movement, an epoxy repair may not
be appropriate unless the movement can be accommodated
by adjacent joints.
Specification requirements for epoxy injection are
contained in ACI 503.7. Refer to ACI 224.1R and ACI
RAP-1 for additional information on epoxy injection of
cracks and other crack repair procedures. Epoxy injection
procedures and techniques in construction are also detailed
in Trout (2006). Refer to International Concrete Repair Institute (ICRI) 210.1 for further information on verifying field
performance of epoxy injection of concrete cracks.
5.2.1.1 Vacuum injection—Cracks may be filled with
epoxy that is drawn in by creating a negative pressure inside
the cracked concrete member. To successfully employ this
technique, all exposed crack surfaces should be sealed sufficiently to create and maintain negative pressure inside the
member.
5.2.1.2 Gravity feed—This technique commonly uses
epoxies or high-molecular-weight methacrylates (HMWM)
poured along the horizontal surface of a crack (Fig. 5.2.1.2).
Flat squeegees are typically used to force the resin into the
35
Fig. 5.2.1—Overhead epoxy injection of crack.
crack. In some situations, an artificial dam with an acrylic
caulk or putty is created for a temporary ponding effect.
Polymer material is poured into the dam, creating a head
pressure to fill the crack. The polymer material and the
caulk need to be removed quickly, before they start to set
up. Failure to remove the excess polymer material and the
temporary caulking will create an undesirable difference of
elevation at the concrete surface. This method is also used
for flood coating. This method is strictly limited to horizontal surfaces. Refer to RAP-2 for additional information
on crack repair by gravity feed with resin, and RAP-13 for
information on methacrylate flood coat.
5.2.2 Injection grouting—Grouting is a common method
for filling cracks, open joints, honeycombed concrete, and
interior voids. Grouting materials include chemical, cement,
polymer, polymer-cement, epoxy, polyurethane, and methacrylate. Grouting can strengthen a structure, stop water
movement, or both. Before selecting a grouting repair
program, the objectives of the grouting should be defined
and the proper material selected to meet those objectives.
Where appropriate, quality control measures should include
taking cores to verify that proper penetration and bond has
been achieved (5.6).
5.2.2.1 Chemical grouting—Chemical grout, as defined in
this guide, is any fluid material not dependent on suspended
solids for reaction. The grout should harden without
adversely affecting any metals or the concrete boundaries
of the opening or void into which it has been injected. From
the standpoint of the user, chemical grouts are typically twocomponent systems requiring blending at or near the point
of injection, or the blending of the injected chemical with
moisture or water existing in the crack or placed there by
the grouting operator (Fig. 5.2.2.1). Chemical grouts may
contain various inert fillers to modify physical properties,
such as consistency, heat generation, and volume. Chapter 4
describes materials for chemical grouting.
Polyurethane chemical grouts are commonly used to
repair leaking cracks, some of which could be leaking a
significant amount of water. These grouts are semiflexible
American Concrete Institute – Copyrighted © Material – www.concrete.org
36
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 5.2.2.1—Chemical grouting.
Fig. 5.2.1.2—Horizontal gravity feed of crack.
and can accommodate some change in crack width without
failure. Polyurethane chemical grouts can treat cracks 0.005
in. (0.12 mm) and greater in width and are injected at high
pressures. Chemical grouts are generally not suitable for
structural repairs.
Chemical grout should be injected from the surface or
interior of the member in the same general manner as cement
grouts with the exception that, for unfilled grouts, the port
sizes may be 1/8 or 1/4 in. (3 or 6 mm) in diameter, and the
port devices may be mechanically anchored or cemented into
place (ACI 224.1R; ACI 503.4; ACI 503.6R; ICRI 340.1).
5.2.2.2 Cement grouting—Grout may be injected into an
opening from the surface of a concrete member or through
holes drilled to intersect the opening in the interior of the
member (Fig. 5.2.2.2). When grout is injected from the
surface, short entry holes or ports, a minimum of 1 in. (25
mm) in diameter and a minimum of 2 in. (50 mm) deep,
are drilled into the opening. The surface of the opening is
sealed between ports with a portland cement or resinous
mortar. Depending on anticipated grouting pressures, short
pipe nipples can be cemented into holes for the grout hose
connections. If the ports are drilled after sealing the openings, a hand-held, cone-shaped fitting on the grout hose may
be adequate for pressure less than 50 psi (350 kPa). Where
cracks or openings extend through a structural member, such
as a wall, the opening is typically sealed and ported on both
sides. When appearance is not a factor, openings may often
be sealed with caulking or with cloth fabric that passes water
Fig. 5.2.2.2—Cement grouting.
or air yet retains solids. Paper and materials that remain
plastic are not suitable for this purpose.
The spacing of the entry ports is largely a matter of judgment based on the nature of the work. As a general rule,
ports should not be spaced farther apart than the desired
depth of grout penetration. Before grouting, the openings
should be flushed with clean water, subject to the same
procedure that is to be used in grouting. Flushing is necessary to wet the interior surfaces for better grout flow and
penetration, to check the effectiveness of the surface sealing
and port system, to provide information on probable grout
flow patterns and interconnections, and to familiarize the
grouting crew with the existing conditions.
Grouting is started at one end of a horizontal crack or
at the bottom of a vertical crack and continues until grout
is observed at the port adjacent to or above the one being
pumped. When this occurs, grout is then injected into the
next port and continues until grout again shows at the adja-
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
cent open hole. Each flowing port should be plugged before
moving to the next injection location. Progress should be
monitored on the far side of the member, if accessible, and
ports or valves should be closed as necessary. Grouting is
typically started with a relatively thin grout, thickened as
quickly as possible to the heaviest consistency that can be
pumped without blockage, as determined by the grouting
operators.
5.2.2.3 Polymer and polymer-cement grouting—Polymer
grouting is typically used to repair dormant cracks 0.25 in.
(6 mm) and greater in width. Polymer grouts can be handapplied and packed into large cracks, regardless of orientation, or they can be poured into cracks in horizontal
slabs. Polymer grouts bond well to concrete and have
low shrinkage, resulting in a watertight repair in dormant
cracks. Similar to epoxy resins, polymer grouts are suitable
for cracks requiring structural repair. If polymer grouts are
used in cracks that experience movement, it can be expected
that parallel cracks may appear adjacent to the repaired
cracks. Materials of varying consistencies are readily available to repair cracks in vertical, overhead, and horizontal
applications.
Polymer-cement grout is a mixture consisting primarily
of cement; fine aggregate; water; and a polymer such as
acrylic, styrene-acrylic, styrene-butadiene, or a water-borne
epoxy. The consistency of this material can be adjusted
from a stiff material suitable for hand-packing large cracks
on overhead and vertical surfaces to a pourable consistency
suitable for gravity feeding cracks in horizontal slabs. These
materials may provide better physical properties such as
bond strength, compressive strength, and flexural strength
than conventional water-based cement grouts that do not
use polymers. The potentially high shrinkage characteristics
of polymer-cement grouts, however, may make it difficult
to obtain a watertight repair when compared with polymer
grouts. Additionally, these materials are not as chemically
resistant as polymer grouts.
5.2.3 Sealants—Polyurethane sealants, also known as
urethane sealants, are formulated for use in sealing both
active and dormant cracks and joints in concrete. Sealants
are commonly used to mitigate the leakage of water through
cracks and joints (Fig. 5.2.3). Various products are available
in numerous colors for use in horizontal or vertical surfaces,
as well as in conditions of continuous water immersion.
These sealants can be used in relatively wide cracks and
joints, generally up to 2 in. (50 mm). Additionally, the movement capability of sealants can accommodate normal dimensional changes in concrete due to structural and thermal
stresses.
Silicone sealants typically have higher elongation properties than polyurethane sealants, making them suitable for
wider and active joints up to 3 to 4 in. (75 to 100 mm). These
sealants are highly resistant to UV light, but should not be
used for immersion applications. All sealants, both polyurethane and silicone, are not suitable for structural repairs.
Additionally, sealants require proper joint design (refer to
ACI 224.1R) to ensure that the materials perform properly,
37
Fig. 5.2.3—Sealant application.
and installation may involve the routing or widening of
smaller width cracks and joints.
5.2.4 Strip-and-seal systems—Strip-and-seal systems
consist of a flexible sheet, such as synthetic rubber, that
spans over a crack or joint and is adhered to the structure
on each side of the crack or joint using a suitable adhesive.
These systems are designed to span over the crack or joint to
prevent leakage of water. These systems may be used to treat
cracks or joints of any width, even though the crack or joint
is not actually filled or repaired. The elongation properties
of these systems are excellent, making them appropriate for
use on active cracks and joints. Some strip-and-seal systems
are highly resistant to UV light; thus, they do not chalk or
weather. Some systems have a high resistance to aggressive chemicals. Generally, these systems do not require any
special worker skills or equipment to install.
Strip-and-seal systems are not suitable for structural
repair; they are designed to be applied to the positive-pressure side of a structure, thus preventing leakage of liquid
into or out of the structure.
Strip-and-seal systems are particularly suited for stopping
water leaks that may otherwise be difficult to seal with other
materials. These systems may be applied vertically, horizontally, or overhead. Refer to ACI 546.3R for additional information on strip-and-seal systems.
5.3—Concrete replacement
5.3.1 Top surface (horizontal repair—partial and full
depth)—Horizontal surface repair is common on elevated
slabs and slabs-on-ground. Delaminated areas are located
by sounding the concrete surface. Performance of top
surface repairs relies on adequate surface preparation; refer
to Chapter 3. Concrete surface moisture conditions should
be as specified by the material manufacturer before placing
the repair material. Top surface repair may also extend full
depth (Fig. 5.3.1), requiring formwork to perform the repair.
Cast-in-place concrete should be cured in compliance with
ACI 301 and proprietary repair materials should be cured
in accordance with manufacturer’s recommendations. Refer
to RAP-7 for additional information on repair of horizontal
concrete surfaces.
5.3.2 Form and pour (horizontal repair)—The form-andpour placement technique is a multistep process consisting
American Concrete Institute – Copyrighted © Material – www.concrete.org
38
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 5.3.1—Horizontal repair at full depth.
of surface preparation of repair area, formwork construction, and placement of repair materials into a confinedspace formwork (Fig. 5.3.2a). Benefits derived from formed
repairs include improved curing due to the protection and
moisture retention provided by the formwork. Watertight
forms should be used to allow for pre-soaking of substrate
and to avoid leakage when using fluid repair mortars. Repair
materials are placed in the cavity between the formwork
and the prepared substrate with buckets, pumps, chutes, or
buggies (Fig. 5.3.2b).
The form-and-pour technique allows the use of many
different cast-in-place repair materials. Placement can
be either a partial- or full-depth repair. Depending on the
consistency of the repair material, consolidation is accomplished by vibration or rodding. When a repair material has
extremely high slump or is self-consolidating, additional
steps to consolidate the repair material may not be required.
High-powered vibrators should not be used to consolidate
fluid repair materials or material with a slump of greater than
7 in. (175 mm). Refer to ACI RAP-4 for additional information on surface repair using form-and-pour techniques.
5.3.3 Form and pump (vertical and overhead repair—
partial depth)—Form-and-pump is a repair method to
replace damaged or deteriorated concrete by filling a formed
cavity with a repair mortar or concrete under pump pressure.
This method can be used for vertical and overhead repairs.
The form-and-pump repair procedure involves constructing
formwork and pumping repair material into the cavity
confined by the formwork and the concrete substrate. The
repair materials are mixed and pumped via a discharge line
into the formwork until the confined cavity is filled. Formwork should be designed and constructed to resist hydrostatic pressure induced by placement and consolidation of
the repair material.
The cavity and formwork design should also provide for
venting of air. Venting can be accomplished by the removal
profile of the prepared concrete, vent tubes, or drilled holes
in the existing concrete. Filling the cavity should begin at
Fig. 5.3.2a—Form-and-pour method.
the lowest point in vertical repairs or at an extremity in overhead repairs. Pumping continues until the material flows
from an adjacent port in the formwork and continues until
the cavity is completely filled (Emmons 1993). Once filled
the forms should be pressurized to 20 to 80 psi (0.14 to 0.55
MPa) depending upon the size, geometry, and number of
venting ports; the repair material is consolidated around the
reinforcing steel and driven into the crevices of the prepared
substrate to improve bond.
Success of this repair methodology is dependent on the
use of proper pumping equipment. Three commonly used
pump technologies are rotor stator, peristaltic, and swing
tube piston. The peristaltic and swing tube piston types are
capable of pumping repair materials containing the large
aggregate necessary for deep or mass placements. Before
work begins, a pre-job meeting and mockup should take
place to assure proper equipment usage. Refer to ACI RAP-5
and ACI 309R for additional information on surface repair
using the form-and-pump technique.
5.3.4 Hand applied (vertical and overhead repair)—The
hand application method can be used to repair deteriorated
concrete or to resurface vertical and overhead concrete
surfaces. Trowel application of repair materials by hand is
suitable for shallow surface repairs, especially in areas with
limited or difficult access.
5.3.4.1 Troweling—The hand-troweling of repair materials
can be used for shallow and limited areas of repair. Trowels
or other suitable tools are used to transport and press the
repair material into the prepared substrate to develop contact
and bond with the existing concrete. These repairs can be
made using portland-cement mortars, proprietary products such as cementitious prepackaged materials, polymercement grouts, polymer grouts, and mortars. Trowel-applied
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
39
Fig. 5.3.2b—Form-and-pour method.
systems should not be used when reinforcing steel is exposed
and undercut due to the difficulty of consolidation of the
repair material around and behind the reinforcing steel. The
paste of the repair material is commonly used as the bonding
material or scrub coat; refer to 5.3.9. Where multiple layers
are needed to obtain the total thickness of the repair, intermediate surfaces should be roughened to help bond subsequent layers. For most applications, the prepared surface of
the repair area should be saturated surface-dry (SSD) at the
time of material application.
A wide variety of proprietary repair mortars and concretes
have been modified with chemicals and thixotropic agents.
The placement techniques recommended by the material
manufacturers do not always conform to accepted placement
techniques for portland-cement mortar and concrete. This is
particularly true for thin sections, such as 1/8 in. (3 mm),
and for vertical and overhead applications. The addition of
chemicals and thixotropic agents that permit deviations in
placement techniques may compromise some performance
properties, including shrinkage, bond strength, and coefficient of thermal expansion. The engineer and contractor
should consult with the manufacturer to ensure that the
material’s performance capability and limitations meet the
project criteria before using these materials.
Successful use of trowel-applied repairs is dependent on
the surface preparation and the skill of the installer. Proper
troweling technique should be used to prevent the entrapment
of air at the bonding surface, which can cause reduced bond
strength. Additionally, proper curing of portland cement
repair mortar is important so that the repair material does not
dry before hydration is complete. Special curing provisions
are advisable for some proprietary repair materials or where
accessibility is difficult (ACI 308R and 308.1). Refer to ACI
RAP-6 for additional information on vertical and overhead
spall repair by the trowel-applied method.
5.3.4.2 Dry packing—Dry packing is the hand placement
of a low-water portland-cement mortar and the subsequent
tamping or ramming of the mortar into place. Because of the
low w/cm, properly proportioned and applied repairs exhibit
low shrinkage, good strength, durability, and watertightness.
Fig. 5.3.5—Shotcrete method.
Due to the extremely low water content of the mortar, curing
becomes even more critical to prevent the loss of moisture
necessary for cement hydration.
Dry packing can be used for repair of form-ties, conebolts, and other holes as well as small areas with relatively
high depth-to-surface area ratios. Because of the labor-intensive nature of this technique, it is not often used for large
repairs.
5.3.5 Shotcrete (vertical and overhead repair—partial and
full depth)—Shotcrete is concrete or mortar pneumatically
conveyed at high velocity through a hose onto a surface (Fig.
5.3.5). The high velocity of the material striking the surface
provides the compactive effort necessary to consolidate the
material and develop a bond to the substrate’s surface. The
shotcrete process is capable of placing repair materials onto
vertical and overhead applications without the use of forms
and can routinely convey material several hundred feet from
the point of delivery.
There are two basic shotcrete processes. In wet-mix shotcrete, cement, aggregate, and water are mixed and pumped
through a hose to a nozzle where air is added to propel the
material onto the surface. Dry-mix shotcrete uses cement
and aggregate that are premixed and pneumatically pumped
through a hose, then water is added at the nozzle as the
American Concrete Institute – Copyrighted © Material – www.concrete.org
40
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
material is projected at high velocity onto a surface. Both
processes place repair materials for normal construction
requirements. In addition to conventional portland-cement
concrete, the shotcrete process can also be used to place
polymer-cement concrete, fiber-reinforced concrete (FRC),
steel or synthetic fibers, and concrete containing silica fume
and other pozzolans. ACI 506R provides information on the
two shotcrete processes and their proper application. Refer
to ACI RAP-12 for additional information on concrete repair
by shotcrete application.
The application of repair materials by the shotcrete
process should be considered when access to the site is
difficult or where significant areas of overhead or vertical
repairs are required. The elimination of formwork provides
economy when compared to other repair techniques. Shotcrete is frequently used for repairing deteriorated concrete
or masonry on bridge substructures, piers, sewers, dams, and
building structures. It is also used for reinforcing structures
by encasing additional reinforcing steel added to beams,
placing bonded structural linings on masonry walls, and
placing additional concrete cover on existing concrete structures; refer to Chapter 6.
The shotcrete nozzle operator’s skill determines the
in-place quality of the repair material. ACI 506.3R provides
a basis for determining the qualifications of a nozzle operator. An ACI-certified, or approved equal, nozzle operator
should be used for the shotcrete operations. A properly
trained nozzleman is necessary to assure proper consolidation of the shotcrete around the reinforcing bars and to avoid
rebounded sand pockets that can lead to reflective cracking.
5.3.6 Low-pressure spraying (vertical and overhead
repair—partial depth)—Low-pressure spray repair materials are typically supplied as prepackaged mortars. The
spray is applied using small concrete pumps or heavy-duty
grout pumps to force the low-slump mortar through a hose.
Air is added at the nozzle to impel the mortar. Bond with
the prepared substrate is achieved through a combination
of proper surface preparation, low-velocity impact, and the
material properties of the prepackaged mortar. Prepackaged
low-slump mortars should not be rapid-setting products
commonly used for hand applications.
Materials should be applied in wet-on-wet lifts. When
conducting the repairs, consideration should be given to
ambient and substrate temperatures. Work stoppages should
be avoided when material is in the hose. Refer to ACI RAP-3
for additional information on spall repair by low-pressure
spraying.
5.3.7 Preplaced aggregate (vertical and overhead repair—
partial depth)—Preplaced-aggregate concrete (PPAC)
involves the placement of coarse aggregate in a formed cavity.
A mixture of portland cement and sand or other appropriate
repair material is then pumped into the formed repair to fill
the voids. Concrete drying shrinkage is reduced because of
point-to-point aggregate contact and reduced paste volume.
Preplaced-aggregate concrete can also be used for horizontal
repairs as long as the grout is injected from the bottom of the
repair either by pumping from underneath the repair area or
using a tremie pipe and withdrawing it as grout fills the area.
Preplaced-aggregate concrete is frequently used on underwater repair projects. The concrete mortar is pumped from
the bottom of the repair, displacing the water as it rises (ACI
546.2R). Information on the preplaced-aggregate method for
concrete construction is provided in ACI 304.1R. In addition, refer to ACI RAP-9 for additional information on spall
repair by the preplaced-aggregate method.
5.3.8 Underwater placement—Placing concrete directly
underwater by means of a tremie or pump is a frequently
used repair method. In general, the same requirements for
material and procedures that apply to new construction also
apply to repairs underwater. These repairs are presented in
ACI 546.2R. Placing concrete under water by tremie and by
pump is covered in detail in ACI 304R.
5.3.9 Bonding repair materials to substrate—Bonding
materials are used to enhance the bond of repair materials
to the existing prepared concrete substrate. Repair materials
may or may not require a separate bonding material. In either
case, the success of the repair depends on achieving intimate and continuous contact between the repair material and
the prepared substrate. This can be achieved by vibration,
pneumatic application, high fluidity, and troweling pressure
in conjunction with maintaining an optimum surface profile
and moisture condition.
In cases where a bonding material is to be used, application of the bonding material to the prepared substrate should
be timed with the placement of the repair material. Bonding
materials applied to substrates may begin setting or curing
prematurely, creating a bond breaker with the repair material.
Cement-based bonding materials are sprayed or broomed,
whereas epoxy- and latex-based systems are brushed, rolled,
broomed, or sprayed (Fig. 5.3.9). Whether the repair material is self-bonding or a bond material is used, tests should
be conducted to ensure that adequate bonding is achieved.
In-place tensile pull-off tests should be performed to evaluate the bond of repair material to the prepared substrate
(ASTM C1583 and ICRI 210.3). This testing provides for
the evaluation of the adequacy of surface preparation, evaluates the tensile strength and bond strength, and assesses the
failure location (5.6).
5.4—Reinforcement repair
The most frequent cause of damage to reinforcing steel is
corrosion. Other possible causes of damage are fire, chemical
attack, and accidental cutting. A licensed design professional
(LDP) should be consulted for any reinforcement repairs.
After deteriorated and damaged concrete is removed, it is
necessary to expose the reinforcing steel, evaluate its condition, and prepare the reinforcement for repair if required.
Proper inspection and preparation of the reinforcement helps
to assure satisfactory long-term performance of the repair
solution.
It is not uncommon that a concrete repair involves
replacing only deteriorated concrete at spalls or delaminations. This approach often leaves chloride-contaminated
concrete surrounding the repair area, creating a highly
conducive environment for continued corrosion of the reinforcement. Such repairs may actually promote corrosion of
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 5.3.9—Application of bonding material before overlay
application.
the reinforcing steel in the surrounding concrete. Deterioration of concrete surrounding a repair area is known as the
halo or anodic ring effect and is discussed more extensively
in Sections 3.2.3.1 and 6.2.5.
5.4.1 Inspection of reinforcing steel—Following concrete
removal, reinforcing steel should be cleaned as described
in 3.3.3 and carefully inspected. Deteriorated or damaged
reinforcement may need to be replaced or supplemented
as directed by the LDP. Project specifications and drawings should include criteria for the repair or replacement of
exposed reinforcement where required, and provide splice
lengths and mechanical connection criteria as required by
ACI 562.
Cleaned reinforcing steel may corrode lightly between the
time it is cleaned and the time that repair material is placed.
If the rust that forms is tightly bonded to the steel such that
it cannot be removed by wire brushing, no action is typically
required. If the rust is loosely bonded so as to inhibit bond
between the steel and the repair material, the reinforcing
bars should be cleaned again before the repair material is
placed. A protective coating may also be applied to the reinforcement after the initial cleaning has been completed; refer
to 5.4.2.3.
Two types of reinforcement commonly used in concrete
structures are mild reinforcing and prestressing steel.
Different repair procedures are warranted for each type of
reinforcement and depend on the condition of the exposed
reinforcement and its impact on structure integrity.
5.4.2 Mild reinforcing steel—For mild reinforcing steel,
repair alternatives can involve the replacement or supplementing of deteriorated and damaged reinforcement. The
method selected is an engineering decision based on the
function of the reinforcement and the required structural
impact to the reinforced member. Refer to 4.6 for different
types of new reinforcing steel available.
41
5.4.2.1 Replacement—One method of repairing reinforcement is to cut out the deteriorated or damaged area
and splice in replacement bars. Great care should be taken
when removing reinforcing steel that is under stress. Avoid
cutting of stressed reinforcement when possible. Unloading
of members may be necessary to relieve stress in reinforcement to remove it safely. Replacement of reinforcement
is common for large repair areas where deteriorated or
damaged reinforcement is totally removed full-length and
replaced with new reinforcing steel of the same size and
length at the same location of the removed reinforcement. It
may be feasible to leave deteriorated or damaged reinforcement in place if one is lap splicing with additional new reinforcing steel adjacent to the deteriorated or damaged area
of reinforcement (4.4.2.2). Replacement sections of new
reinforcement should match the size of the existing reinforcement and be welded or coupled to the cut ends of the
existing reinforcement. If welded splices are used, welding
should be performed in accordance with ACI 318 and the
American Welding Society (AWS D1.4). All welding should
be performed by an AWS-certified welder to the requirements of AWS D1.4. Butt welding should be avoided due to
the high degree of skill required to perform a full penetration weld because the back side of the bars are not always
accessible. Caution should be taken for welded splices on
bars larger than No. 8 (No. 25) because the heated embedded
bars could expand and crack the surrounding concrete.
Special attention is necessary when welding bars adjacent to
unbonded or bonded prestressing steel. Another method of
splicing bars is to use mechanical connections. ACI 439.3R
describes commercially available proprietary mechanical
connection devices. Mechanical connections should meet
the requirements of ACI 318.
5.4.2.2 Supplemental reinforcement—This alternative is
often selected when the reinforcement has lost significant
cross-sectional area, the existing reinforcement is inadequate,
or the existing member is to be strengthened. The allowable
loss of cross-sectional area of the existing reinforcing steel
and the decision to add supplemental reinforcement should
be evaluated by the LDP on a case-by-case basis following
ACI 562 criteria. The deteriorated or damaged reinforcement to remain should be cleaned in accordance with 3.3.3
and the concrete removed to allow placement of the supplemental bar beside the existing bar with adequate cover and
a minimum of 3/4 in. (19 mm) space below bars. The length
of the supplemental bar should equal to the length of the
deteriorated segment of the existing bar plus a lap splice
length on each end equal to the lap splice requirements for
the smaller bar diameter of the two bars, as specified in
ACI 318. Supplemental bars may also be lap welded to the
existing bars in accordance with AWS D1.4. When supplemental reinforcement is placed to strengthen a section, the
techniques discussed in Chapter 7 should be considered.
Supplemental reinforcement can also be installed to control
shrinkage of the repair material, restore structural capacity,
and provide mechanical anchorage of the concrete repair
materials if a bond failure occurs. Mechanical anchorage
is particularly important for repairs to building façades and
American Concrete Institute – Copyrighted © Material – www.concrete.org
42
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 5.4.3.2a—–Failure of unbonded tendon.
Fig. 5.4.2.3—Coating reinforcing steel.
overhead repairs. For the installation of supplemental reinforcement, embedment into the existing concrete may be
required. The effectiveness of grouts to embed supplemental
reinforcing steel in hardened concrete should be evaluated
(Best and McDonald 1990).
5.4.2.3 Coating of reinforcement—New uncoated bars and
existing bars that have been cleaned may be coated with an
epoxy, polymer-cement slurry, zinc-rich epoxy, cementitious coating, latex cement, or acrylic latex for protection
against corrosion (Fig. 5.4.2.3). Some materials may require
multiple coats, but in general the coating should be applied
at a total thickness less than 12 mils (0.3 mm) to minimize
loss of bond development at the deformations. Reinforcing
bars that have lost original deformations as a result of corrosion and cleaning will have reduced bond with most repair
materials. Coating of these bars with materials such as epoxy
further reduces their bond with repair materials. Care should
be taken during the coating process to avoid spillage onto
the substrate concrete, as epoxy or zinc-rich coatings act
as a bond breaker between the new repair material and the
existing concrete. Materials such as polymer-cement coatings may contain corrosion inhibitors for further protection
of the reinforcing steel and may also act as bonding materials
for bonding the new repair material to the existing concrete.
Embedded galvanic anodes are also used for protection
against corrosion instead of coatings.
5.4.3 Prestressing steel—Prestressing steel in structural
members is of two basic types: bonded and unbonded. Deterioration or damage to prestressing steel can result from
impact, overload, corrosion, or fire. Fire can soften coldworked, high-strength prestressing steel, altering its strength
and hardness, resulting in possible failure. Repair options for
bonded strands are different than those for unbonded strands
and wires. For external repair and strengthening options,
refer to Chapter 7.
5.4.3.1 Bonded strands—For prestressed bonded strands,
only the exposed and damaged or deteriorated section is
detensioned during repair. The repair procedure requires
replacing the damaged or deteriorated section with new
strand connected to undamaged or nondeteriorated ends of
the existing strand. The new strand section for the exposed
length should be post-tensioned to achieve the force level of
the existing bonded strand. Refer to ACI 423.8R for further
information on the repair of grouted multi-strand and bar
tendon systems.
5.4.3.2 Unbonded systems—Unbonded systems include
buttonhead (wires) and monostrand (strand) tendons.
Strands are installed inside sheathings (paper wrapping for
wire systems) embedded in the concrete member. Strands
are protected against corrosion by the sheathing, corrosioninhibiting material such as grease, or both. However, if the
grease did not completely fill the annular space between the
strand and sheathing, the grease did not contain adequate
rust-inhibiting properties or the sheathing was loose-fitting,
unbonded strands or wires are susceptible to corrosion and
deterioration. Corrosion of the strand or wires and anchorages has been the primary cause of unbonded tendon failure
(Fig. 5.4.3.2a). Shoring in the span being repaired and adjacent spans up to several bays away may be required before
and during unbonded system repair. Unbonded strands and
wires may need to be detensioned before repair and retensioned after repair to restore the structural integrity of the
member.
Unbonded tendons (monostrand system) can be tested to
determine the existing force in the strands and to assess their
ability to support the design load. This can be performed at
the live end by attaching a chuck and coupler to an exposed
end of the strand, following the removal of the grout pocket
and performing a lift-off test. This test may require at least
1.5 in. (40 mm) of rust-free strand at the grout pocket.
An in-place strand tension test can also be performed to
measure the tensile forces in the strands (Fig. 5.4.3.2b).
PTI DC80.3-12/ICRI 320.6 (PTI/ICRI 2012) provides guidance for the evaluation of unbonded post-tensioned concrete
structures.
To perform a repair, the deteriorated portion of a tendon is
exposed by removing the concrete and sheathing. The strand
or wires are then detensioned and cut on both sides of the
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
deteriorated portion where sound strand or wires are evident.
Use caution when detensioning and cutting the tensioned
or partially tensioned strands or wires. The installation of
a lock-off device (monostrand system) may be necessary
to maintain forces in the strand beyond the repair area and
enable the repair to be completed. The deteriorated portion
Fig. 5.4.3.2b—In-place tension testing of unbonded tendon.
43
of the tendon that is removed and replaced with a new
section is then spliced to the existing tendon at the location
of the cuts. The repaired strand or wires are then stressed
to provide the required forces in the tendon (Fig. 5.4.3.2c).
Tendon repair techniques use both buttonhead and monostrand hardware/equipment, as well as combination systems,
depending on the type of unbonded system in the structure.
Encapsulated anchorages and other waterproofing devices
should be considered for unbonded system repairs to provide
added corrosion protection (Fig. 5.4.3.2d).
Removal of a deteriorated or damaged unbonded strand
(monostrand system) from the sheathing is possible, but
sometimes difficult. Strands of the same diameter should be
used for the repair, if possible. When the tendon is removed
for replacement, it may be necessary to insert a smallerdiameter strand of higher-strength material that is capable of
achieving the required stressing force in the tendon.
Refer to ACI 423.4R and PTI DC 80.3-12/ICRI 320.6
(PTI/ICRI 2012) for further information on the repair of
unbonded post-tensioned concrete structures.
5.5—Anchorage
Anchors are often used in conjunction with reinforcement
repair to prevent dislodging of the reinforcing steel from the
substrate concrete in the event of a bond failure. Anchors
are commonly used in the repair of overhead and vertical
surfaces, such as façades, to ensure that the repair area does
not dislodge from the structure. Noncorrosive anchors, such
as stainless steel anchors, are often specified for repair areas
susceptible to corrosion, especially in areas of inadequate
concrete cover.
There are two general categories of anchoring systems:
post-installed and cast-in-place (ACI 355.1R).
5.5.1 Post-installed anchors—Post-installed anchor
systems use anchors installed in predrilled holes. These
Fig. 5.4.3.2c—Tendon splices in place (left) and being restressed (right).
American Concrete Institute – Copyrighted © Material – www.concrete.org
44
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 5.4.3.2d—Unbonded tendon anchors removed (left). Encapsulated replacement
anchors shown secured in place prior to recasting in concrete (right).
anchors can be divided into two general types: bonded and
expansion anchors.
5.5.1.1 Bonded anchors—Bonded anchors include both
grouted (headed bolts or a variety of other shapes installed
with a cementitious grout) and chemical anchors (typically
threaded rods installed with a two-part chemical compound
that is available as glass capsules, plastic cartridges, tubes or
bulk). These anchor systems develop their holding capacities by the bonding of the adhesive to both the anchor and
the concrete along the wall of the drilled hole (McDonald
1989). Chemical systems such as epoxies, polyesters, and
vinyl esters, have different setting and performance characteristics that should be considered when specifying to meet
design intent. The LDP should be diligent when specifying
chemical anchors in an underwater or moist environment
by verifying that the chemical adhesive has been tested and
satisfactorily performs in a representative environment.
Epoxy anchors may have significant limitations when used
at elevated temperatures, such as in the case of a fire, particularly if the anchor is in tension. The use of epoxy anchors
for supporting sustained loads should be avoided because
of creep issues (FHWA 2008). Performance characteristics
of adhesive anchoring systems should be evaluated before
using adhesive anchors in sustained tensile-load applications
(McDonald 1998; NTSB 2007).
5.5.1.2 Expansion anchors—Expansion anchor systems,
sometimes called mechanical anchors, include torque and
deformation-controlled and undercut anchors. These anchors
develop their strength from friction against the side of the
drilled hole, from keying into a localized crushed zone of
the concrete resulting from the setting operation or from a
combination of friction and keying. These types of anchors
develop bursting forces in the concrete. Edge distances and
the spacing between anchors should be sufficient to prevent
cracking. For undercut anchors, strength is derived from
keying into an undercut at the bottom of a drilled hole. Refer
to ACI 355.2 and ACI 318 for additional information on
post-installed mechanical anchors in concrete.
5.5.1.3 Anchorage of reinforcement into existing
substrate—When repair design requires anchors for additional or supplemental reinforcement, or additional reinforcement is anchored into the substrate concrete, care
should be taken to thoroughly clean the inside of drilled
Fig. 5.5.1.3—Coring.
holes. Two methods of drilling holes are rotary percussion
and core drilling (Fig. 5.5.1.3). Each method requires a
different means of cleaning and preparation.
a) Rotary percussion—This method uses electric or
pneumatic drills for hole drilling that typically create large
amounts of dust and concrete fines. Care should be taken to
remove all dust and fines using compressed air, vacuums,
sandblasting, or water blasting. Standard pneumatic drills
use a hollow drill rod through which the cuttings are continuously expelled from the hole, resulting in a clean, roughsurfaced hole. In addition, the use of a chisel-tipped bit
will produce relatively larger cuttings. Conversely, electric
hammer drills do not expel the cuttings, but rather beat them
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
45
Fig. 5.6.4—Pull-off testing.
up into a fine dust that adheres to the wall of the hole, requiring
further cleaning. If water blasting is used, care should be taken
to not leave slurry residue inside the hole. This method creates
a slightly roughened profile inside the hole.
b) Core drilling—Core-drilled holes create several conditions that need to be addressed before installing bonded
anchors. Core drilling produces slurry that may compromise
the bonding surface when it dries within the drilled hole.
Additionally, cored holes typically create a smoother surface
than rotary percussion-drilled holes. The combination of
water blasting, vacuuming, air-blasting, and/or sandblasting
may be necessary to remove the slurry and roughen the
inside surface of cored holes.
5.5.2 Cast-in-place anchors—Cast-in-place anchor
systems include embedded, non-adjustable anchors of
various types and shapes, bolted connections, and adjustable
anchors set in place before placing concrete.
5.5.3 Anchor strength—Anchor strength and long-term
performance depend on a variety of factors that should be
evaluated, including:
a) Yield and ultimate material strength;
b) Hole diameter and drilling system used;
c) Embedment length;
d) Annular gap between the anchor and the drilled hole for
post-installed anchors;
e) Concrete strength and condition;
f) Type and direction of load application (static, dynamic,
tension, shear, bending, or combined loading);
g) Spacing to other anchors and edges;
h) Temperature (for chemical and epoxy anchors);
i) Hole cleaning;
j) Mode of failure of the anchor system (concrete breakage,
steel breakage, slip or pullout);
k) Environmental conditions for moisture and corrosion
resistance and creep.
Reference Appendix D of ACI 318-11.
Site testing for verification of performance should be
conducted for critical applications. For chemical anchors,
tests should be performed to determine the long-term
creep performance at the highest expected service load and
temperature. For all anchor systems, the manufacturer’s
installation instructions should be followed to ensure proper
anchor performance.
5.6—Quality control and assurance
Quality control and assurance procedures are necessary
during and after placement of the repair material. Various
testing and evaluation methods (ACI 228.2R and ICRI
210.4) can provide valuable information relative to the
success of the repair. Performance monitoring of repairs
should also be considered. Some common test methods and
evaluation techniques performed during and after repairs are
outlined in the following.
5.6.1 Mockups—Sample repairs should be performed so
that the owner, contractor, and LDP can agree on repair
procedure, quality of repairs, and the post-repair aesthetics
before starting the repair program. This step will reduce
unrealistic expectations as to the performance and appearance of the repair areas.
5.6.2 In-place testing—Testing should be performed for
quality control of repairs and may include strength testing,
delamination, and debonding identification, and internal
cracking and void detection of the repair materials. Test
methods that establish the presence of deterioration or
damage can also be used to determine that the identified
condition is no longer present after repair.
5.6.3 Coring and laboratory testing—Coring of existing
repair areas may be used to perform accelerated aging or
petrographic analysis for assessing durability of the concrete
repair material. Physical tests on cores can also be used to
determine strength characteristics of the repair.
5.6.4 Pull-off testing (ASTM C1583 and ICRI 210.3)—
Tests can be performed to assess the quality of bond and
determine bond strength of the repair material (Fig. 5.6.4).
These tests can be used to determine if repairs meet specified
bond strength requirements and verify that surface preparation is adequate.
CHAPTER 6—PROTECTIVE SYSTEMS
Protective systems consist of materials and methods which
extend the service life of concrete structures by reducing
their exposure to moisture and other factors, reducing corrosion of metals embedded in concrete, increasing surface
abrasion or impact resistance, or improving the structure’s
resistance to other deleterious influences. Protective systems
limit the intrusion of moisture, chloride ions, and contami-
American Concrete Institute – Copyrighted © Material – www.concrete.org
46
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
nants into the concrete by using surface treatments or minimize corrosion by electrochemical principles.
6.1—Introduction and selection factors
The primary reason for providing a protection system is
to extend the life of the structure or subsequent repairs. A
repair program should determine the causes for concrete
deterioration or failures such that the protection systems can
be designed to improve the performance of the repairs as
well as the original concrete by moderating the underlying
causes of concrete deterioration.
There are a multitude of methods and materials available
to protect concrete. Refer to International Concrete Repair
Institute (ICRI) 320.2R or ICRI 330.1 for additional information. The following factors should be included in the decision-making process for the appropriate protection system.
6.2—Typical problems that can be mitigated with
protection systems
When developing the protection system for a project, the
factors affecting the performance of the original concrete
and completed repairs should be evaluated. Misplaced reinforcing steel, low concrete cover, high chloride content, lowquality concrete, cracking, and carbonation are some factors
that contribute to corrosion of embedded reinforcing steel. A
protective system should be designed to reduce the effects
of these factors and should minimize the effects of detrimental conditions that could result in a failure of the repairs
or contribute to other concrete deterioration. The following
are some common problems that should be considered in a
repair program.
6.2.1 Low-quality concrete or inadequate concrete
cover—The performance of any concrete structure is, in part,
a function of the quality and cover of concrete in that structure. High-quality, durable, properly consolidated concrete
with adequate cover provides an environment that should
protect the embedded reinforcing steel for years without any
protection system before repairs are required. Conversely,
low-quality concrete with deficiencies such as excessive
cracking and honeycombing, voids, lack of consolidation,
inadequate entrained air-void system, or otherwise substandard conditions, contribute to the corrosion of the reinforcing steel as well as to other types of deterioration of
the structure. It is best to remove deteriorated concrete as
part of a repair program, when and where possible. A properly selected protection system can improve the durability
of low-quality concrete, enhance the performance of good
concrete, and extend the life of repairs.
6.2.2 Misplaced reinforcing steel—Misplaced reinforcing
steel is a major contributing factor to corrosion (ACI 222R).
This commonly occurs at reveals on walls or columns, in
exposed slabs with variable thickness at the edge and at
hooked bars perpendicular to exposed concrete slab edges,
if the reinforcing steel is placed too close to the surface. The
repair program may provide for the lack of cover over the
reinforcement. This can be accomplished with build-outs,
where appropriate. Barrier coatings on the reinforcing steel
or concrete surface, frequently in combination with other
techniques, can provide added protection against corrosion.
Cathodic protection, chloride extraction, and corrosioninhibiting additives in repair materials may also be useful to
provide added protection against corrosion.
6.2.3 Water penetration—Water may penetrate into
concrete by hydrostatic pressure, moisture vapor pressure, capillary action, wind-driven rain, or any combination of these. Cracks, porous concrete, structural defects, or
improperly designed or constructed joints all contribute to
the penetration of moisture into concrete. Water penetration
into or through concrete can contribute to corrosion of reinforcement, freezing-and-thawing damage, leakage into the
interior of the structure or occupied levels beneath decks,
contamination of potable water, contamination of groundwater from wastewater or hazardous wastes, and possible
structural damage.
6.2.4 Carbonation—Carbonation is the reduction of the
alkalinity of concrete caused by the absorption of carbon
dioxide and moisture into the concrete. In normal concrete,
the reinforcing steel is protected by the naturally high alkalinity of the concrete around the reinforcement, typically
at a pH greater than 12. At this pH, a passivating oxide
layer is formed around the reinforcing steel that acts as a
protective coating. The oxide coating helps prevent the
reinforcing steel from corroding as long as sufficient alkalinity is maintained. When carbonation occurs, the alkalinity
falls and, once it is below a pH of approximately 10, the
embedded reinforcing steel is subject to corrosion. Because
carbonation occurs from the exposed surface of the concrete
inwards, bars close to the exterior surface are subject to the
effects of carbonation. Barrier coatings may reduce the rate
of additional future carbonation. Other systems available to
reestablish the protection of the reinforcing steel in carbonated concrete include the use of a cathodic protection system
or the realkalization of concrete.
The carbonation of concrete that contains chlorides may
cause the release of chloride ions from Freidel’s salt. Friedel’s salt is an anion exchange mineral. It has affinity for
anions such as chloride and is capable to retain them to a
certain extent in its crystallographical structure. This release
of chloride ions may create a chloride front ahead of the
carbonation front. Also, background chlorides reduce the
passivation of steel such that concrete containing chloride,
even below the chloride threshold, requires a higher pH
for passivation of steel. Carbonated structures that are also
contaminated with chlorides may therefore experience more
severe corrosion.
6.2.5 Anodic ring (halo effect)—The anodic ring (halo
effect) refers to corrosion of reinforcing steel, and subsequent concrete deterioration, in the parent concrete around
the perimeter of a concrete repair. This type of deterioration
is the result of corrosion of existing reinforcement extending
from the parent concrete into repair concrete caused by
chemical differences between the parent concrete and the
repair concrete. It occurs because steel is present in two
distinctly different environments, setting up conditions that
can result in differences in electrical potential between the
new and the parent concrete. Corrosion and concrete delami-
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
nation typically occurs in the parent concrete adjacent to the
repair.
Reinforcement corrosion, due to the anodic effect, is a
difficult problem to solve. Sealers or barrier coatings help
slow down the process but they do not stop it. Barrier coatings on the reinforcing steel, such as epoxies, latex slurries, or zinc-rich coatings, can inhibit the corrosion activity;
however, there are, in addition to high labor costs, challenges
with field application that can reduce their effectiveness.
Problems can include access to coating the bar undersides
and dripping of coatings, which later act as bond-breakers
on substrate surfaces. Passive cathodic protection techniques
such as the use of embedded galvanic anodes around the
perimeter of repairs can delay the onset of the anodic ring
effect.
6.2.6 Surface erosion—Erosion of concrete at the surface
is a major concern on dams, spillways, and other waterfront
structures, as well as on bridge decks, ramps, parking decks,
industrial floors, and other traffic-bearing structures. To a
lesser extent, it can also be a concern on buildings exposed
to acid rain or other severe weather conditions. Concrete
overlays, surface hardeners, sealers, or other treatments are
often used to protect these surfaces after the completion of
any required repairs (ACI 210R and 210.1R).
6.3—Total system concept
When selecting a protection system for a particular structure, factors affecting the performance of that system on the
structure should be considered. Depending on the type of
structure, some of the possible factors to consider include:
a) Protective materials;
b) Interface of protective materials to concrete surface;
c) Surface and bulk properties of the concrete;
d) Structural considerations;
e) As-built construction considerations such as placement
of reinforcement;
f) Exposure of concrete to the elements;
g) Stability of ground-supporting concrete;
h) Groundwater pressures;
i) Chemical exposures;
j) Exposure to abrasion, erosion, and cavitation;
k) Exposure to potable water;
l) Exposure to wastewater or hazardous wastes;
m) Environmental considerations.
6.3.1 Economic factors—Evaluation of various protection
systems should consider their life-cycle costs. The protection system with the lowest initial cost may actually be more
expensive when the costs of future repairs are evaluated over
the projected life of the structure.
6.3.2 Service record—Proven systems with documented
track records and field performance histories generally
provide expected results. New systems in the market typically have limited track records and the field performance
may be more difficult to predict.
6.3.3 Appearance—Protective systems may alter the
appearance of a structure and mockups can be used to assess
the appearance. Appearance should be considered when
selecting an appropriate repair and protection system.
47
6.3.4 Construction quality monitoring—A quality control
program should be established and implemented during the
installation of the protection system.
6.3.5 Environmental considerations—The Environmental
Protection Agency (EPA) or other regulatory agencies may
have volatile organic compound (VOC) requirements, as
well as other requirements, that should be considered when
selecting protection systems. In addition, the handling, use,
and disposal of hazardous chemicals can be a factor when
evaluating potential protection systems. Noise, fumes, and
dust levels can also be selection factors.
6.3.5.1 Protective systems that are in contact with potable
water should meet the testing requirements of National
Science Foundation (NSF)/ANSI 61, as appropriate for the
size limits of the repair.
6.3.6 Compatibility and bond—The surface conditions
should be reviewed when selecting a protective system.
Factors to consider include the compatibility of the repair
and substrate materials with the materials of the protective system as well as the ability of the protection material
to bond to existing coatings or repair materials. The bond
of any remaining existing coatings should be evaluated in
accordance with ICRI 210.3 or ASTM C1583. Surface preparation requirements as well as the need to remove existing
coatings or sealers may influence the selection of a new
system. Job-site testing, laboratory testing, or both, should
be performed before installing a new protection system over
existing coatings or sealers (ICRI 310.2R).
6.3.7 Durability and performance—The anticipated
performance and service life of a protection system, coupled
with the owner’s requirements, should be considered
before selecting a system. Among the factors to consider
are substrate movement, thermal expansion and contraction, freezing and thawing, exposure to wind-driven rain,
carbon dioxide exposure, ultraviolet exposure, temperature
variations, moisture variations, acid rain, abrasion, chemical
exposure, and any other potentially destructive conditions.
6.3.8 Safety requirements—The environment where a
system is installed can influence the selection of that system.
Not only should performance characteristics be considered
but so should safety issues. Many protection materials are
toxic and could cause medical problems to some people
during installation. An obvious concern is for the safety of
the construction crews during the application, especially
in poorly ventilated spaces. People not involved with the
installation but who are in direct proximity, spaces with open
flames, potential for sparks from nearby electrical service,
and other hazards are issues that should be considered. The
contractor should follow proper safety procedures at all
times. The manufacturers should be part of the process when
decisions are made regarding installation and the safe use of
their products. Material safety data sheets (MSDS) should
be furnished with all supplied materials and made available
to the owner.
6.3.9 Resistance to chemical attack—Review chemical
resistance, testing, and performance records for protective systems that are required to resist exposure to corrosive chemicals or gases to verify that they can perform
American Concrete Institute – Copyrighted © Material – www.concrete.org
48
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
adequately. References include ACI 350.1; ACI 515.2R;
Portland Cement Association (PCA) IS001 (PCA 1997);
Society for Protective Coating (SSPC) PA 7 and SSPC-Paint
38; SSPC TR 5, TU 2, and TU 10; as well as specific manufacturer’s recommendations.
6.4—Surface treatments
Surface treatments are intended to provide protection to
the concrete. They include materials applied to the surface
of concrete, reinforcing steel, or both. Although the materials and procedures discussed in this section are important
components of a protection system, they are not the only
components that should be evaluated to achieve an adequate
protection system for a repair program. Most of the protection systems for repaired concrete require at least one, or in
some cases several, of the surface treatment classifications
discussed in 6.5.2 and 6.6 to 6.9.
6.4.1 Uses—Surface treatments include horizontal and
vertical applications. The techniques and materials selected
should be consistent with the intended use. The objective
is to limit corrosion by establishing conditions that reduce
the existing moisture level in the concrete by reducing or
preventing further moisture, chemical, and chloride intrusion.
6.4.1.1 Precautions—Compatibility among the intended
treatment, repair materials, and the existing concrete
substrate, with moisture, chemical and chloride intrusion,
should be considered. Compatibility of materials in contact
with each other should be evaluated to avoid bond or performance failure of the surface treatment materials or the
underlying substrate.
Surface treatments often rely on bond to perform
adequately. Encapsulating concrete between non-breathing
surface treatments should be avoided. Manufacturer’s
recommendations and limitations should be followed.
In addition, other factors that could influence the effectiveness of the surface treatment should be evaluated. For
example, adjacent construction not included in the scope of
work for the surface treatment may be a potential source for
water infiltration. This may include adjacent masonry, unrepaired or repaired concrete, window systems, intersecting
walls or slabs, roofs, decks, intersecting or continuous
waterstops, or any other construction that could reduce the
performance of the protection system.
6.4.1.2 Properties—The properties of surface treatments
affecting their selection are discussed in the following
sections and are summarized in Table 6.4.1.2a. A particular
product should only be selected based on its field performance and results of standardized or comparative tests.
Studies that directly measure performance with respect
to water absorption, durability in northern and southern
climates, and resistance to reinforcement corrosion are
discussed later in this section. Table 6.4.1.2b gives references to standards for sealers and coatings.
6.4.1.3 Installation requirements—Most surface treatments should be applied to a clean, dry, and sound substrate
at moderate temperature and humidity conditions in a wellventilated space. A relatively smooth surface is needed for
liquid-applied membranes. Because these conditions do
not always prevail, the difficulty and cost in achieving the
appropriate installation conditions may influence the choice
of a system.
Before applying most surface treatments, concrete repairs
should be completed and allowed to cure. Most manufacturers require a minimum curing period of 28 days for
cast-in-place concrete. Product manufacturers should be
consulted for the required curing time and application conditions for specific products.
Details of terminations at expansion and contraction
joints, door and window openings, drains, and curbs should
be reviewed and installed properly. It is imperative to ventilate any flammable or noxious fumes that may be produced.
Specifications should include installation requirements.
6.4.1.4 Performance characteristics—Surface treatment
systems, and the materials used in those systems, have
their own characteristics. Although several of the available
systems might provide adequate protection to the concrete
and embedded reinforcing steel, there might be certain
parameters for a given project that make one more attractive than another. Before evaluating the available protection
systems, determine the required system characteristics for
the project. The system should then be selected based on
its ability to satisfy project requirements. The following are
many of the primary system characteristics that should be
reviewed when selecting a protection system. Table 6.4.1.2b
lists most of the tests commonly used to evaluate performance characteristics.
a) Water permeability—Resistance to water absorption is
a critical factor in protective systems, as water can facilitate the penetration of chemical or salt solutions causing
corrosion of the reinforcing steel. Water permeability is a
measurement of the quantity of water that can pass through a
surface treatment over a period of time and can be measured
using RILEM Test No. II.4.
b) Moisture vapor transmission—Surface treatments
should resist water intrusion, but they should also allow
concrete to dry, particularly if placed over new concrete
repairs or on the inside face of foundation walls or slabs-onground. Moisture vapor transmission is the quantity of water
vapor that can pass through a protective system over a period
of time. References include ASTM E96 and ACI 302.2R.
c) Crack bridging—The protection system should include
treatment of cracks that could provide paths for moisture or
other liquids into the concrete substrate. Surface treatment
products included in 6.5.2 have varying crack bridging abilities. Some products have the ability to fill small dormant
cracks but are not suitable to bridge active cracks. Certain
products are formulated to bridge small, active cracks if
detailed properly. The capacity of the selected products to
bridge cracks should be carefully reviewed. If necessary,
incorporate additional methods into the protection system to
treat the cracks.
d) Skid and slip resistance—Skid and slip resistance are
measures of the frictional characteristics of the surface.
Penetrants generally do not affect the skid resistance of
concrete because they are located at or beneath the surface
where they are subject to wear to the same extent as the
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
49
Table 6.4.1.2a—Summary of surface treatments
Types
Penetrating sealers
Surface sealers
Generic
classification(s)
Installation requirements
Alkyl-alkoxy-silane/ Surface free of pretreatments;
siloxanes
Sprayed, brushed, or rolled;
Ventilation required.
Epoxy/urethane/
methacrylate
Corrosion inhibitors Various types
Coatings (high-build Epoxy
and elastomeric)
Urethane
Rubberized
asphaltic
Overlays
Concrete;
Polymer concrete;
Polymer-modified
concrete.
Clean, dry, and sound surface;
Sprayed, brushed, rolled, or
squeegeed.
Clean, dry surface
free of pretreatments;
Ventilation may be required;
Generally above freezing.
Clean, dry, and sound surface;
Sprayed, brushed, rolled or
squeegeed;
Approximately 50 F (10 C) or
above;
Ventilation required;
Level surface typically required.
Clean, sound, and roughened
surface;
Hand or machine applied;
Generally above freezing;
Ventilation may be required.
concrete surface. Surface sealers and high build coatings
may make the concrete surface less skid-resistant, whereas
membrane systems with embedded aggregate and overlays
have the potential to create more skid-resistant surfaces.
Refer to Table 6.4.1.2a.
e) Appearance—Most surface treatments alter the concrete
appearance. Some systems, which can mask the contrast
between the original concrete and the repairs, can be advantageous if appearance is an important factor.
f) Carbonation resistance—Some surface treatments are
effective at resisting the penetration of carbon dioxide and
can provide protection against carbonation.
g) Volatile organic compound characteristics—Federal
and state regulations have set allowable VOC levels that
may not allow for use of certain surface treatments in some
areas.
6.4.2 Surface treatment classifications—The surface treatment classifications discussed in this section are commonly
used for concrete repair and protection against reinforcement
corrosion. Because of the number or combination of products and techniques, it is impossible to cover all of them.
In addition, new products and methods to protect concrete
are continually being developed and introduced to the
market. Surface treatments in this section are grouped into
the following general classifications: penetrating sealers,
surface-applied corrosion inhibitors, surface sealers, highbuild coatings, elastomeric coatings, and overlay general.
6.4.2.1 Penetrating sealer
a) Description—Penetrating sealers are materials that,
after application, are generally contained within the nearsurface region of the concrete and include water repellent
agents. Depth of penetration varies by the product and with
Durability characteristics
Improves resistance to freezing
and thawing;
Reduces salt penetration;
Reduces rate of corrosion;
Reapplication required.
Variable UV radiation resistance;
Prevents moisture from
penetrating cracks;
Reapplication required.
Reduces rate of corrosion if
sufficient material penetrates the
concrete to the reinforcing steel.
Performance characteristics
Improved resistance to water absorption and reinforcement corrosion;
Does not bridge cracks;
Breathable.
Seals cracks;
Improved resistance to water absorption and reinforcement corrosion;
Does not bridge active cracks;
Water vapor barrier.
Reduces rate of corrosion if sufficient
material penetrates the concrete to the
reinforcing steel.
Generally improves resistance to
freezing and thawing;
Fair to good abrasion resistance;
Variable UV radiation resistance.
Generally good resistance to water
absorption.
Flexible materials bridge small
cracks;
Water vapor barrier.
Improves resistance to freezing
and thawing;
Excellent abrasion resistance.
May add weight;
Architectural finish is possible;
Protects structural concrete and
reinforcement;
May improve structural capacity.
the properties of the concrete on which the sealer is applied.
Depth of penetration is a function of the size of the sealer
molecule, the pore structure in the concrete, and the moisture content of the concrete. While deep penetration may be
desirable, especially for surfaces subjected to abrasion, it is
not the most important criterion for sealer effectiveness.
These sealers are formulated to provide protection as
water repellents or as surface hardeners. Penetrating sealers
do not have crack-bridging capabilities; however, the hydrophobic properties imparted by some of these products may
reduce the intrusion of moisture into narrow cracks. Products in this classification generally do not alter the appearance of the concrete surface, although some might change
the color slightly. Repairs, cracks, and any other flaws on the
surface will not be masked by penetrating sealers.
Such sealers include, but are not limited to, silanes, siloxanes, penetrating epoxies, and methacrylates. Some sealers
penetrate but are not effective damp-proofers.
b) Uses—The products in this classification have the capability to reduce the intrusion of water, chlorides, and, in
some cases, mild chemicals. Many permit the transmission
of water vapor.
c) Applications and limitations—Penetrating sealers may
be applied by roller, squeegee, or spray to the concrete
substrate. Proper surface preparation is important for
successful application due to the sensitivity of penetrating
sealers to contaminants and previously applied sealers in the
substrate. UV resistance, wear resistance, and abrasion resistance are generally good when compared with coatings or
membrane systems
6.4.2.2 Surface-applied corrosion inhibitors—Topically
applied corrosion inhibitors in concrete repair were first
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
50
Table 6.4.1.2b—Testing of sealers and coatings for
reinforced concrete
A. Protective properties
1. Artificial or accelerated
weathering
2. Water absorption
3. Chloride ingress
B. Durability
1. Natural weathering
2. Artificial or accelerated
weathering
3. Salt spray resistance
4. Freezing and thawing/scaling
5. Resistance to alkali
6. Light stability
7. Chalking
8. Water swelling
9. Resistance to wind-driven
rain
10. Coefficient of friction
11. Chemical resistance
12. Crack bridging
C. Physical properties
1. Viscosity
2. Hardness
3. Specific gravity
4. Drying time
5. Nonvolatile content
6. Flash point
ASTM D1653 and ASTM E96
ASTM C67 and ASTM C642
AASHTO T 259
ASTM D4141
ASTM D2565
ASTM B117
ASTM D2247
ASTM D1647
ASTM D333
ASTM D4214
ASTM D4214, ASTM D2247
ASTM E514, Federal Specification
TT-C-555B, Federal Specification TT-P-1411A, ASTM D412,
ASTMD522, ASTM D2370, ASTM
D429, ASTM D2197, ASTM D3359,
ASTM D4541, ASTM D2794
ASTM D2047
ASTM C267
ASTM C836
ASTM D2196
ASTM D1471, ASTM D2134, ASTM
D2240, ASTM D3363
ASTM D1640
ASTM D1353
ASTM D56, ASTM D93, ASTM
D3278
introduced in the early 1990s. To be effective, these materials must migrate through the concrete to the reinforcing
steel so that they can mitigate the steel corrosion. The effectiveness and life expectancy of these materials is unknown,
and likely vary considerably with different types of inhibitors, the properties of the concrete, and site conditions. Users
report a wide variation in their effectiveness, which presents
the question as to what parameters relate to successful use
for any given formulation. A number of studies of their effectiveness have been completed with variable results (Berke et
al. 1992; Jones et al. 1999; Elsner 2000; Elsner et al. 1997,
1999; Mietz et al. 1997; Transportation Research Board
2001). Unfortunately, there is no easy or universal method
of determining if the corrosion inhibitor has penetrated to
the level of the reinforcing steel because each product has
its own detection method. Manufacturers should include in
their literature the corrosion inhibitor type, recommended
uses, application rates, constraints, anticipated effectiveness,
penetration detection method, and monitoring method.
6.4.2.3 Surface sealers
a) Description—Surface sealers are products that create
a film of 10 mils (0.25 mm) or less in thickness that generally adhere to the concrete surface. The dry film thickness
of surface sealers ranges from 1 to 10 mils (0.03 to 0.25
mm). Although these products can be pigmented or naturally colored, some are transparent, which results in a wet or
glossy appearance. They may or may not appreciably alter
the texture of the surface, and most surface blemishes typically reflect through the sealer. Although surface sealers do
not have significant crack-bridging capabilities, some might
fill dormant cracks, reducing the penetration of moisture
through those cracks.
Such products include epoxies, urethanes, methacrylates,
and acrylic resins. Certain oil-based or latex-based paints,
such as styrene-butadiene, polyvinyl acetate, acrylic, or
blends of these with other polymers dispersed in water,
would be included in this classification if less than 10 mils
(0.25 mm) thick (PCA 1995).
b) Uses—Products in this classification have the capability
to reduce the intrusion of water, chlorides, and, in some
cases, mild chemicals. They may also inhibit the transmission of water vapor to varying degrees.
c) Application and limitations—The materials may be
applied with brush, roller, squeegee, or spray. The chemical
carriers within some of the products may cause application
limitations. The manufacturer’s safety recommendations
should be followed. Surface sealers, in general, reduce skid
resistance. Many of these products are affected by UV light
exposure and will wear due to surface abrasion. Some of
these products depend on solvents to work and may have
problems meeting VOC regulations. Newer formulations
that meet VOC regulations do not have many years of
in-service usage.
6.4.2.4 High-build coatings
a) Description—High-build coatings are materials with
a dry film thickness greater than 10 mils (0.25 mm) and
less than 30 mils (0.75 mm) applied to the surface of the
concrete. High-build coatings alter the appearance of the
surface, may be pigmented, and may partially mask blemishes in the concrete surface.
Base polymers of such products include, but are not
limited to, acrylics, alkyds, styrene butadiene copolymers,
vinyl esters, chlorinated rubbers, urethanes, methacrylates,
silicones, polyesters, polyurethanes, polyurea, and epoxies.
b) Uses—These products are generally used for decorative or protective barrier systems. Some products in this
classification may be suitable for use against wind-driven
rain, salts, and mild chemicals.
c) Applications and limitations—These products may be
applied with brush, roller, squeegee, or spray. For exterior
environments, the coating should be resistant to oxidation
and UV light and exposure. On floors, resistance to abrasion,
punctures, and mild chemicals such as salts, grease, oil, and
detergents are also important.
In addition to the durability of the coating material, the
bond between the coating and concrete substrate should
remain intact. Even with proper surface preparation, the
bond can break down. If the coating is highly impermeable
to water vapor, water may condense at the concrete-coating
interface or lead to critical saturation and rapid deterioration
of the concrete by cycles of freezing and thawing.
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Epoxy resins are commonly used coating materials that
generally have good bonding and durability characteristics.
The resins can be mixed with fine aggregates to improve
abrasion and skid resistance. When used in horizontal applications, some high-build coatings, including epoxies without
aggregate, may result in a very slippery surface when wet
and may not be suitable for pedestrian or vehicular traffic.
Non-elastomeric high-build coatings generally do not bridge
active cracks but may be effective in filling small, dormant
cracks. These products have better wear characteristics than
thinner systems.
A coating intended to reduce reinforcement corrosion in
repair work may also be required to waterproof the structure,
protect against chemical attack, or improve the structure’s
appearance. Breathability is often an important factor when
selecting a protection material on exterior walls and slabson-ground. There are high-build coatings formulated for use
in decorative systems that have high permeability to water
vapor while providing sufficient protection against liquid
water intrusion.
6.4.2.5 Elastomeric coatings
a) Description—Elastomeric coatings are surface treatments with thicknesses greater than 30 mils (0.75 mm)
and less than 250 mils (6 mm) applied to the surface of the
concrete. These products alter the appearance and mask
blemishes in the concrete surface.
Elastomeric coatings generally have sufficient thickness
and flexibility to bridge narrow, inactive cracks of various
widths, even if the crack width fluctuates. Some systems
require that cracks wider than 10 to 15 mils (0.25 to 0.375
mm) be routed and sealed before applying the membrane.
Elastomeric membranes are typically gray or black, but
some manufacturers offer other colors. Colored coatings
have a tendency to fade, especially when exposed to ultraviolet light. Refer to ACI 362.1R, 362.2R, and 350.1.
Such products include, but are not limited to, urethanes,
acrylics, neoprenes, and asphaltic products. Slabs-onground should not receive a coating that is also a vapor
barrier. An impervious barrier allows moisture passing
from the subgrade or backfill to accumulate under or behind
the barrier, causing debonding of the coating or leading to
critical saturation and rapid deterioration of the concrete by
cycles of freezing and thawing.
b) Uses—Elastomeric coatings are generally used as
protective or waterproofing systems. Elastomeric coatings
can also be used as damp-proofing systems.
c) Application and limitations—When in liquid form,
these products may be applied by brush, squeegee, roller,
trowel, or spray. Preformed sheets are sealed at the edges to
form a continuous waterproofing membrane. Most of these
membranes are resistant to water absorption and bridge
active or inactive cracks less than 0.01 in. (0.25 mm) wide.
Membranes with an aggregate-filled urethane or epoxy
resin top coats offer reasonable skid and abrasion resistance
under traffic. Frequent maintenance of exposed membranes
in parking structures may be required at steep ramps and at
turning, starting, and stopping areas. The gritty surfaces of
some membrane top coats intended for abrasion and skid
51
resistance are difficult to keep clean and may wear off, or
be damaged by mechanical means such as tears caused by
snow plows.
Tests that measure performance characteristics of elastomeric membranes, particularly traffic deck membrane
systems, are quite limited. Manufacturers may list a variety
of different non-standardized test results in their technical
data sheets. When available, standardized test results from
independent laboratories for traffic-bearing membrane
systems should be compared for key performance characteristics such as permeability, elongation, tensile strength, tear
strength, adhesion, modulus of elasticity, abrasion resistance,
low temperature flexibility, and water-vapor transmission.
6.4.2.6 Overlays general
a) Description—Overlays are products 250 mils (6 mm)
or greater in thickness that can be bonded or unbonded to
the surface of the concrete. Such products include but are
not limited to polymer concrete, portland-cement concrete,
epoxies, polyesters, polymer-modified concrete, and other
hydraulic-cement concrete overlays. Overlays change the
appearance, texture, and elevation of the original concrete
surface. The thickness of an overlay can be used to improve
the drainage characteristics of the top surface of a concrete
slab. Overlays may bridge inactive cracks; however, active
cracks may mirror through the overlay.
b) Uses—Overlays may be used as a wearing course and
generally provide protection against the intrusion of water
and chloride ions. Overlays may also be used to strengthen
or restore structural capacity. Overlays also provide abrasion
resistance and may be decorative (ACI 222R; 345R; 548.4;
548.5R).
c) Application and limitations—Overlays may be placed,
troweled, screeded, sprayed or seeded in one or more layers
onto the concrete surface. Because an overlay adds mass
proportional to its thickness, the additional dead load weight
should be considered in the analysis of the structure. Overlays can be installed to act compositely with the structure.
Additional reinforcement may be added, such as weldedwire reinforcement, reinforcing steel, or fibers.
For an overlay to perform properly, the surface to which
it is bonded should be clean, sound, and roughened.
Laitance, dust, films formed from hydrodemolition concrete
removal, and debris should be removed. Concrete placement
against construction joints on the concrete substrate should
involve proper surface preparation as per manufacturer’s
recommendations.
Cracking has been a problem in some bonded overlays.
Existing cracks can reflect through thin overlays; therefore,
bonded overlays should not be used in situations where there
is active cracking or structural movement. Unbonded overlays should be used in these situations instead.
Slabs-on-ground in freezing climates should not receive
an overlay that also acts as a vapor barrier. An impervious
barrier allows moisture passing from the subgrade or backfill to accumulate under or behind the barrier, debonding the
overlay or leading to critical saturation and rapid deterioration of the concrete by cycles of freezing and thawing.
American Concrete Institute – Copyrighted © Material – www.concrete.org
52
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Thin cementitious overlays may be susceptible to plasticshrinkage cracking because of their high surface-to-volume
ratio, which promotes rapid evaporation under accelerated
drying conditions such as low relative humidity and wind.
Also, because these concretes typically have low w/cm, there
is little bleed water to replace evaporated water. Environmental conditions to be expected when placing overlays
should be determined and early morning or nighttime placements should be considered to avoid accelerated drying
conditions.
Cracking in bonded overlays may be caused by tearing
the surface due to late finishing operations; plastic shrinkage
due to rapid drying; differential movement between the
deck and the overlay due to temperature differences; or
drying shrinkage or existing cracks propagating through the
overlay. Refer to ACI 224.1R for information on cracking.
Testing of the in-place concrete should be done before and
after surface preparation to determine the modulus of rupture
of the concrete and, after the overlay has been completed, to
determine bond strength. The direct tensile test, as described
in ACI 503R, ICRI 210.3, and ASTM C1583, should be
specified.
6.4.2.6.1 Common overlay systems
a) Unbonded—Unbonded overlays are used to provide
wearing courses and for creating slopes for drainage over
waterproofing membranes. They also can provide architectural treatments for exposed decks or driveways. Asphalt,
asphaltic concrete, or concrete are generally used for this
purpose (ACI 546.1R).
Asphalt and asphaltic concrete overlays are porous and do
not provide waterproofing by themselves. The absence of an
effective waterproofing system below an unbonded asphaltic
or concrete system can promote deck deterioration due to
freezing and thawing, as well as lead to corrosion-related
damage due to penetration of water and chlorides into the
concrete.
These systems are typically used on bridge decks, plaza
decks, parking garages, and over-occupied spaces.
b) Bonded portland-cement concrete (PCC) overlay—
Bonded PCC overlays are typically relatively thin layers of
horizontal concrete placed on a properly prepared existing
concrete surface to restore a spalled or disintegrated surface
or to provide a protective barrier. Portland-cement concrete
overlays are sometimes fortified with fibers and other additives (4.2.1 and 4.2.5). Low-slump concrete overlays are also
included in this group (4.2.7). Bonded PCC overlays provide
a protective barrier to deicing salts and sometimes increase
the load-carrying capacity of the underlying concrete. The
thickness of an overlay may range from 1.5 in. (40 mm) to
almost any reasonable thickness, depending on the purpose
it is intended to serve.
A PCC overlay may be suitable for a wide variety of
applications, such as resurfacing spalled or cracked concrete
surfaces on bridge decks or in parking structures, increasing
cover over reinforcing steel, adding slip resistance, or
leveling floors. Other applications of overlays include repair
of concrete surfaces damaged by abrasion, freezing, fire, and
the repair of deteriorated pavements.
Low-slump concrete overlays are PCC overlays that have
modified mixture proportions to produce a denser, more
durable concrete. They have good bond characteristics to a
properly prepared substrate and increased durability because
of a lower w/cm. Portland-cement concrete overlays are less
expensive than modified concrete systems. The performance
of low-slump concrete overlays depends on workmanship
and effective use of conventional materials. Generally,
the performance of these systems has been good. Local
bond failures have been reported, but these have typically
been attributed to inadequate surface preparation or other
construction deficiencies (ACI 222R; 546.1R; PCA 1996).
Low-slump concrete overlays and other PCC overlays are
susceptible to cracking, especially on continuous span structures. Portland-cement-based overlays should not be used in
any application in which the original damage was caused by
chemical attack that would continue to attack the portland
cement in the overlay.
c) Latex-modified concrete (LMC) overlays—Latex-modified concrete is similar to conventional concrete except
that it contains a polymer dispersion (latex) and less water.
The rate of 15 percent latex solids to portland cement by
mass has been most commonly used in bridge and parking
deck overlays. The water in the latex constitutes part of the
water required to hydrate the cement, and the latex provides
supplementary binding properties to produce a concrete with
a low w/cm, good durability, good bonding characteristics,
and a high degree of resistance to penetration by chloride
ions (4.2.5).
There have been problems associated with finishing LMC
overlays. Hot weather and wind cause rapid drying, making
finishing difficult and promoting shrinkage cracking.
Mixing, placing, and finishing should be completed within
30 minutes to accommodate the coalescing of the latex.
Failure to do so may lead to tearing of the latex film that
is forming within the concrete. Mixing the LMC should be
done in a mobile mixer. Concrete mixed in a concrete truck
or drum-type mixer should be limited to 3 minutes of mixing
after the latex has been added. As such, it is generally not
practical to mix LMC in concrete trucks because the LMC
will likely lose its workability before it can be discharged
and placed. Longer periods of mixing entrap air and subsequently increase total air content. The result can be significant reductions in compressive strength and abrasion resistance. Placement at night can help minimize these problems.
Another problem is if the application of grooves, or texturing,
is applied too soon, the grooves will collapse. If texturing is
delayed until after the latex film forms, the surface tears, and
cracking often occurs. Refer to ACI 548.3R, ACI 548.4, ACI
222R, and Section 4.3.1.
Latex-modified concrete overlays, prepared with a rapidhardening cement such as calcium sulpho aluminate dicalcium silicate, can be used when it is desirable to place traffic
on the overlay with as little as 3 hours of cure (Sprinkel
2011). Latex-modified concrete overlays are generally used
as wearing and protective barriers on bridge and parking
garage decks and in damp-proofing or decorative systems on
plaza decks and parking garages.
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
d) Polymer concrete overlays—Polymer concrete is a class
of composite materials that includes a wide group of mortars
and concretes. The polymer families most commonly used in
polymer concrete overlays are epoxies, polyesters, and vinyl
esters. The compositions of each of these polymer binders
are different. Whereas more than one may be used for most
applications, some are more suitable for specific situations.
Refer to ACI 548.5R and Section 4.3.2.
Overlays of polymer concrete are typically bonded to a
prepared substrate and provide a durable and wear-resistant
surface. They may be formulated to provide low permeability
to water, chemicals, and chloride ions. This helps prevent
deterioration of the concrete due to cycles of freezing and
thawing and chemical attack. These materials have good
bonding characteristics to properly prepared substrates. The
bond in tension and shear of the product selected should be at
least equal to the tensile and shear strength of the substrate.
The surface texture can be made to provide skid-resistant
and hydroplaning-resistant surface characteristics within
acceptable limits (ACI 548.1R; ACI 548.5R).
An important advantage of polymer concrete compared to
other overlay systems is its rapid cure characteristic. This can
minimize disruptions and traffic control costs and improve
the scheduling of repairs. In addition, polymer-concrete
overlays can be installed without expensive equipment.
A disadvantage is that they should be applied to dry
surfaces. The workability and curing rate depend on application temperatures (ACI 548.1R; ACI 548.5R). Another
disadvantage is that polymer concrete generally has a
different thermal expansion coefficient than PCC.
Polymer-concrete overlays are generally used as a wearing
course in damp-proofing or decorative systems. Polymerconcrete overlays have been used as wearing and protective
barriers for bridge decks and parking garage decks (ACI
548.8; ACI 548.10; Fowler and Whitney 2011).
e) High-performance concrete overlays—High-performance concrete is designed to have improved physical
properties with the addition of chemical admixtures, supplemental cementitious materials, and other modifiers such as
microfibers or macrofibers, fly ash, silica fume, and blastfurnace slag. Chemical admixtures may include high-range
water-reducing admixtures, shrinkage-reducing admixtures,
and expansive agents. The improved properties are generally
related to improved workability or placeability in the short
term or durability and resistance to normal types of deterioration in the long term. They include lower permeability to
moisture and chemicals, reduced shrinkage, higher strength,
crack resistance, and resistance to freezing and thawing.
Silica-fume concrete is a normal portland-cement concrete
containing silica fume as a supplemental cementitious material. Silica-fume concrete is commonly used as an alternative to LMC or low-slump concrete. Silica-fume concrete
overlays retard the intrusion of chlorides by providing a
denser, less-permeable matrix. In addition, these overlays
are more abrasion-resistant, have increased early and ultimate strength, and improved bond to the substrate (4.2.1.3).
53
Silica-fume overlays are used as a wearing course on
bridge and parking garage decks and as a protective barrier
to structural concrete in aggressive chemical environments.
Silica-fume concrete is susceptible to cracking from
autogenous drying and plastic shrinkage. If the silica fume is
added to the concrete mixture at the end of the batch cycle, it
may act as a retarding admixture. Adding silica fume to the
mixture makes it sticky and, thus, more difficult to finish.
The use of a high-range water-reducing admixture may be
required.
6.5—Concrete surface preparation and installation
requirements
Certain basic conditions should be met before application
of the protective system. Of these conditions, surface preparation is one of the most important.
6.5.1 Completion of concrete repairs—Concrete repairs
should be completed and cured typically 28 days before
application of a protective system (ACI 302.2R). Some
product manufacturers claim that certain products can be
installed on moist surfaces and in considerably less time
than 28 days.
6.5.2 Surface preparation—The surface should be clean
and dry in most cases, but manufacturer’s recommendations
should also be followed. A damp surface may be preferable
for hydraulic-cement concrete (HCC) overlays, as this may
enhance the cure. The substrate should generally be sound,
and all surface contamination, including poorly bonded
existing coatings, should be removed. The bond of existing
coatings, which may have deteriorated due to their age,
should be evaluated. Surface preparation should remove all
poorly bonded existing coatings, which could result in poor
adhesion of a new coating.
Accepted techniques include scarification, brushing or
grinding, abrasive blasting, and shotblasting. Dust, debris,
and microfractured or bruised concrete resulting from surface
preparation should be removed before applying the surface
treatment. Refer to Chapter 3 for more detail on surface
preparation. ICRI 310.2R provides guidelines for the preparation of concrete substrates that could be used to define a
standard of acceptability for some protection systems.
6.5.3 Surface profiles for liquid-applied membranes and
other coatings—Surfaces should be relatively smooth, typically in the range of ICRI 310.2R concrete surface profile
of CSP 3 to CSP 5 (ICRI 310.2R; SSPC-SP13/NACE 6).
Most liquid-applied products are not intended to level off
or hide imperfections, although trowel grade materials can
sometimes be used for this purpose. The surface profile can
compromise the protective qualities of coatings. Surface
profiles should be considered when applying coatings to
assure that the minimum dry film thickness is maintained.
This may entail the application of additional material and
could be an issue for exposed membranes or coatings where
appearance is a concern. Proper surface preparation should
be implemented, including the repair of shallow delaminations, surface scaling, and aggregate popouts; grinding of
rough surfaces; or the treatment of any other surface defects
as required to achieve proper product performance.
American Concrete Institute – Copyrighted © Material – www.concrete.org
54
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
6.5.3.1 Surface quality—For liquid-applied membranes
and other coatings, the quality of the concrete surface should
be evaluated before installation. Not only should the surface
be free of contaminants that could affect the performance of
the protection system, it should also have adequate strength,
a pH that is compatible with the product to be installed, and
as other physical and chemical properties required by the
manufacturer for the selected protection system. Refer to
SSPC-SP13/NACE 6 for an overview of the tests commonly
used to check the surface quality.
The membrane or coating manufacturer should be
consulted to establish criteria for acceptability of the
prepared surface.
6.5.4 Ventilation requirements—Ventilation requirements and humidity conditions should be considered when
selecting products so that proper application and curing can
occur safely and in accordance with requirements. Many
surface sealers and penetrants have a high solvent content
that, because of evaporation during curing, will require
ventilation to remove the vapors from the structure to ensure
the safety of construction personnel and other occupants.
6.5.5 Temperature limitations—Most products have installation limitations related to the substrate temperatures, rate
of temperature change, product temperature, and mixing and
setting times. These limitations should be considered when
scheduling work.
6.6—Joints
Joint sealants in concrete minimize the intrusion of liquids,
solids, or gases, and protect the concrete against damage.
In certain applications, secondary functions are to improve
thermal and acoustical insulation, dampen vibrations, or
prevent unwanted matter from collecting in crevices (ACI
504R).
Protection systems for joints include the sealing of cracks,
contraction joints, expansion joints, and construction joints.
6.6.1 Types of joints
a) Cracks—Cracks occur in concrete because of shrinkage,
thermal changes, structural-related stresses, and long-term
strain shortening. Before selecting a sealant, the reason for
the cracking should be determined. Active or moving cracks
should be identified. In some instances, structural bonding
of a crack may be required to restore structural integrity,
whereas for most active cracks, restraint across the crack
should be avoided because future movement will cause a
rigid repair to crack again or create a new crack nearby.
b) Contraction joints—Contraction joints are purposely
installed joints designed to regulate cracking that occurs due
to the contraction of concrete (ACI 224.3R). Often called
control joints, they are intended to control crack locations by
creating a plane of weakness in the structure. The necessary
plane of weakness may be formed by reducing the concrete
cross section by tooling or saw cutting a joint.
c) Expansion (isolation) joints—Expansion joints prevent
crushing and distortion including displacement, buckling,
and warping, and provide separation between abutting
concrete structural units. Such crushing and distortion can
be due to the transmission of compressive forces that may be
developed by expansion, applied loads, or differential movements arising from configuration of the structure or its settlement (ACI 504R). Expansion joints are made by providing
a gap between abutting structural units. This gap is often
bridged by some sort of mechanical or elastomeric joint or
other device to allow movement.
d) Construction joints—Construction joints are made
before and after interruptions in concrete placement or
through positioning of precast units. Locations are typically
predetermined to limit the work that can be done at one time
to a convenient size with the least impairment to the strength
of the finished structure. Construction joints may also be
necessitated by unforeseen interruptions in concreting
operations. Depending on the structural design, they may be
required to function later as expansion or contraction joints,
or they may be required to be solidly bonded together to
maintain complete structural integrity. Construction joints
may run horizontally or vertically, depending on the placing
sequence prescribed by the design of the structure (ACI
504R).
6.6.2 Sealing methods—Methods to seal joints include
injection techniques, routing and caulking, bonding,
installing premolded seals, or installing appropriate surface
protection systems such as elastomeric membranes, as
discussed in 4.3 and 6.4.2.5. ACI 504R discusses different
techniques and materials to seal joints, and ACI 503.4
discusses epoxy materials.
6.7—Cathodic protection
6.7.1 Description—Reinforcing steel in concrete is generally protected from corrosion by a passive oxide film formed
by contact with alkaline cement. When aggressive ions,
such as chlorides, contaminate the concrete around the reinforcing steel, or if dissimilar metals are present, the passive
oxide film may be weakened or destroyed, and accelerated
corrosion of the reinforcing steel can occur.
Corrosion is an electrochemical process where anodic and
cathodic areas are formed on the steel. When the anodic and
cathodic areas are electrically continuous and in the same
electrolyte, an electric current flows from the anodic area to
the cathodic area, which results in corrosion at the anodic
areas. Unless mitigated, corrosion continues until failure
occurs at the anodic area. ACI 222R contains additional
information on corrosion of steel in concrete.
Cathodic protection is a proven procedure to control the
corrosion of steel in contaminated concrete. The basic principle involved in cathodic protection is to make all of the
embedded reinforcing steel cathodic, thereby preventing
further corrosion of the steel. This can be accomplished by
electrically connecting the reinforcing steel to another electrically conductive material that becomes the anode with or
without the application of an external power supply.
Cathodic protection systems in which an external power
supply is not used are called sacrificial, galvanic, or passive
systems. The metal that is used to protect the steel is less
noble or more prone to corrosion than the steel. Examples
are, zinc, magnesium, and aluminum alloys. The sacrificial
metal oxidizes in place of the steel and the steel is protected
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
(NACE 01105). An impressed current cathodic protection
(ICCP) system incorporates an external power supply to
force a small electric current to flow to the reinforcing steel
to counteract the current created by the corrosion process.
A highly corrosion-resistant metal such as platinum or titanium typically serves as the anode in most ICCP systems.
Refer to ACI 222.3R and NACE 01102 for additional information on this subject.
6.7.2 Applications—Cathodic protection can be used to
protect almost any type of reinforced concrete structure.
6.7.3 Limitations—Cathodic protection systems can mitigate corrosion on many types of structures; however, the
following should be observed:
a) Cathodic protection does not replace corroded steel;
b) Cathodic protection using impressed-current systems
should not be used for general use on prestressed or posttensioned concrete structures. Hydrogen embrittlement of
the high-strength steels may occur;
c) Post-tensioned structures may be cathodically protected
using passive sacrificial systems after an analysis by a corrosion engineer;
d) The reinforcing steel needs to be electrically continuous for cathodic protection to function. Electrical continuity of the reinforcing steel should be confirmed during
system installation. In structures where the reinforcement is
covered with an inorganic coating such as epoxy, electrical
continuity of the reinforcement is likely to be problematic
and should be confirmed before considering the installation
of a cathodic protection system;
e) For an ICCP system to function, the reinforcing steel
should remain completely isolated from any contact with the
anode system. Electrical contact between the anode and the
reinforcing steel will create a short circuit and compromise
the operation of the system (SHRP-S-337).
Operation of a cathodic protection system requires the
concrete to work as an ionically conductive medium. As
such, the concrete must have suitable resistivity and moisture content to be sufficiently conductive.
6.7.4 Types of sacrificial passive cathodic systems
a) Zinc hydrogel anode—Zinc sheet anodes, precoated
with a conductive hydrogel adhesive, are applied to the
concrete surface. Various coatings or architectural layers can
be applied over the anode for aesthetics.
b) Sprayed zinc or zinc alloys—Sprayed zinc or zinc alloys
are applied to the concrete using metallizing equipment such
as arc spray or flame spray. Enclosure during spraying may
be desired to address toxicity and environmental concerns.
This system has been used in both marine and nonmarine
environments. A chemical activator or humectant may
be applied to the metallized surface to increase current
output and corrosion protection for structures in nonmarine
environments.
c) Zinc anode jackets and overlays—Zinc mesh may be
installed in concrete jackets in marine tidal zones. Distributed
zinc anodes may be installed in concrete jackets, overlays,
and in holes drilled into the existing structure. Anodes may
be chemically activated to increase current output and corrosion protection for structures in nonmarine environments.
55
d) Embedded galvanic anodes—Embedded galvanic
anodes generally provide localized galvanic protection. They
are attached to the reinforcing steel and are embedded within
the repair concrete. The anodes are primarily installed along
the perimeter of concrete patch repairs and along joints to
protect adjacent areas from corrosion due to the anodic-ring
effect. The anodes can also be installed on a grid pattern or in
drilled holes to provide more overall protection (ACI RAP-8).
6.7.5 Types of ICCP systems—All ICCP systems contain
an anode, a DC power source, and connecting cables. In
addition to basic components, there may be reference electrodes or other monitoring and measuring devices. The
primary difference between the types of systems is the anode
installation and its application.
a) Mesh-type noble metal anodes—A mesh of a noble
metal anode is fixed to the concrete with multiple pins and
then covered with a cementitious material.
b) Ribbon-type noble metal anodes—A ribbon of a noble
metal anode. Generally, these anodes are grouted in slots
with a suitable material.
c) Conductive coatings—Carbon-filled conductive
coating/mastic has been used as a surface-applied anode.
Some of these systems have failed prematurely if exposed
to wet conditions.
d) Conductive ceramic anodes—Conductive ceramic
anodes are installed and grouted into drilled holes.
6.8—Chloride extraction
Chloride extraction can be accomplished by an electrochemical process.
6.8.1 Description—Electrochemical chloride extraction
(ECE) is a treatment process where chloride ions are removed
from chloride-contaminated concrete through ion migration.
At termination of the treatment process, the entire system
is removed from the structure. Unlike a cathodic protection
system, there is no permanent system or components to be
maintained or operated for the life of the structure.
The benefits of ECE include reduced corrosion activity,
extended service life, and elimination of the need to remove
and replace chloride contaminated concrete. Electrochemical
chloride extraction can be applied to vertical and horizontal
concrete surfaces. Minimal disruption of traffic on bridge or
parking decks occurs if a temporary traffic-bearing surface
is incorporated. Refer to ACI 222.3R and NACE 01101 for
additional information.
6.8.2 Electrochemical chloride extraction application—
To remove chlorides from a reinforced concrete structure,
an anode embedded in an electrolyte media, typically a
poultice similar to paper maché, is applied to the concrete
surface. The anode and reinforcing steel in the concrete
are connected to the two terminals of a DC power supply
such that the anode is positively charged and the reinforcing
bar is negative. Chloride ions, being negatively charged,
migrate toward the anode, which is the positive electrode.
Because the anode is external to the concrete, the chloride
ions leave the concrete and accumulate in the electrolyte
media around the anode. Thus, the chloride content of the
concrete is reduced, particularly around the negatively
American Concrete Institute – Copyrighted © Material – www.concrete.org
56
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
charged reinforcing steel. At the end of the treatment period,
the anode and the electrolyte medium that contains the chlorides are removed from the surface of the concrete. While
the chlorides are being removed, the electrolytic production
of hydroxyl ions at the reinforcing steel surface results in a
high-pH zone around the steel. Therefore, when the process
is terminated and the installation is removed, the reinforcing
steel is in a low-chloride, highly-alkaline concrete environment. The result is a strong repassivation of the embedded
reinforcing steel. Corrosion of the reinforcing steel should
be significantly reduced. Protection of the concrete may be
recommended to keep external chlorides from infiltrating
the concrete.
Electrochemical chloride extraction generally takes
between 3 to 8 weeks to complete. The treatment duration is affected by a number of factors, including treatment
current density, quantity and distribution of chloride ions,
reinforcing steel quantity, and concrete properties such as
permeability and electrical resistivity. All required structural
repairs should be implemented either before or after completion of the ECE process.
6.8.3 Limitations—Electrochemical chloride extraction
can be used to mitigate corrosion on many types of structures; however, the following should be observed:
a) Electrochemical chloride extraction does not replace
corroded steel;
b) Electrochemical chloride extraction should not be used on
prestressed or post-tensioned concrete elements as hydrogen
embrittlement of the high-strength steels may occur;
c) The reinforcing steel should be electrically continuous
for ECE to function;
d) The effect of the removal may be different in areas
close to reinforcing steel than it is in areas further away from
the reinforcing steel.
6.9—Realkalization
Realkalization is a process used to increase the pH of
carbonated concrete.
6.9.1 Description—Realkalization is an electrochemical
treatment process whereby the pH of carbonated concrete
is increased. At the termination of the treatment process the
entire system is removed from the structure.
The benefits of realkalization include reduced corrosion
activity, extended service life, and elimination of the need to
remove and replace carbonated concrete. Realkalization can
be applied to both vertical and horizontal concrete surfaces.
Refer to ACI 222.3R and NACE 01104 for additional information on this subject.
6.9.2 Application—The realkalization process is essentially similar to ECE with two differences:
1) The treatment time for realkalization is much shorter
than ECE, typically 3 to 10 days;
2) Realkalization is completed using an alkaline electrolyte solution.
6.9.3 Limitations—Limitations for realkalization are
similar to those for ECE.
CHAPTER 7—STRUCTURAL REPAIR AND
STRENGTHENING
7.1—General
Repairs that serve to reestablish the capacity of a member
are deemed to be structural. This chapter discusses considerations when repairs are intended to be structural to both
restore and enhance the capacity of concrete members. Prior
to repairing structural members, a structural analysis may
be required to determine if the members are overloaded or
underdesigned for the service loads and for ultimate loads.
The analysis should consider serviceability and strength
and should include consideration of the causes of the structural failure or degradation; refer to ACI 562. Based on
the evaluations and analytical results, the engineer should
decide whether repair is intended to restore the original load
capacity only or whether repair is intended to strengthen the
member beyond its original capacity, possibly due to additional service loads or code upgrades. ACI 562 provides
guidance for structural evaluation and repair design.
Sections 7.2 through 7.7 outline several acceptable
alternatives for strengthening structural members without
completely replacing them. These sections concentrate on
construction methods used for strengthening, including
placement of reinforcement within existing concrete sections
as well as placement of new reinforcement outside of the
existing member. In all cases, the goal is to strengthen the
member to resist stresses caused by flexure, shear, torsion,
and axial forces so that it meets the required minimum
strength.
7.2—Internal structural repair (restoration to
original member strength)
7.2.1 Repair of cracks by epoxy injection—In cases where
repair is needed to restore the original capacity without
further increasing the member’s structural strength capacity,
epoxy injection is commonly used, provided the crack is not
actively moving or overly contaminated with dirt or mineral
deposits (Fig. 7.2.1). Because the epoxy tensile bond to the
concrete substrate is stronger than the concrete’s tensile
strength, subsequent loads applied to the injected concrete
section may result in failures at the same load as that of the
original uncracked member section. Resin injection by itself
is therefore not a strengthening method, but is considered
a restoration method that returns the section to its original
precracked strength. Refer to 4.3, 5.2, ACI 503R, and International Concrete Repair Institute (ICRI) 210.1.
Strengthening of cracked members may be accomplished
by installing additional reinforcement across the crack plane
in combination with resin injection. Frequently, internal
or external reinforcement is installed in combination with
epoxy injection to strengthen a member beyond its original
capacity.
7.2.2 Advantages and typical uses—Injection can be
successfully performed on cracks as narrow as 0.13 mm
(0.005 in.) in width using epoxy injection resins conforming
to the appropriate grade, type, and class of ASTM C881.
Narrower cracks, down to approximately 0.05 mm
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
57
of recracking from thermal stress fluctuations. In addition,
cured epoxy properties such as creep resistance and modulus
of elasticity should be considered.
Fig. 7.2.1—Epoxy injection of crack in wall.
(0.002 in.), can be injected with epoxy or other polymer
systems having a viscosity below 200 cps (ACI 503R and
ACI 224.1R). Applying negative pressure to the crack with a
vacuum pump can increase the penetration of resin into long
or narrow cracks.
7.2.3 Disadvantages—Special considerations should be
made for bond strength when elevated in-service temperatures are anticipated. Epoxies lose stiffness and strength
when exposed to fire or sustained elevated temperatures
above approximately 120 to 150°F (50 to 65°C).
Although some epoxies are moisture-insensitive and thus
suitable for injection into wet or damp cracks, epoxies may
not be appropriate for injection into cracks that have water
actively flowing through them. The specifier should obtain
independent test results to verify the moisture sensitivity of
the specific epoxy proposed for use, depending on the actual
installation conditions. Even epoxies labeled water-insensitive may develop milky white bond lines during curing
if injected into excessively wet cracks, indicating that the
epoxy is being affected by the moisture. Verification that the
epoxy is completely water-insensitive should be made by
injecting the test epoxy into prewetted cracks, then evaluating a cored sample of the cured epoxy injected into the
crack. Some epoxies absorb water, which reduces the epoxy
stiffness and increases creep deformations.
7.2.4 Other considerations—Shrinkage cracking that
occurs in slabs or walls as a result of restraint at support
ends may develop into full-depth cracks. This type of
cracking may result from volume change during concrete
curing (drying) or from wide thermal fluctuations. The cause
of cracking should be considered when selecting an epoxy
injection repair and eliminated if possible. The slab or wall
shrinkage cracking described above may recur after injecting
the cracks unless end restraints are removed to accommodate slab or wall movement.
Concrete temperature at the time of repair should be
considered. Variations in thermal conditions can result in a
buildup of internal stresses at the epoxy bond line. Injecting
the crack while the member is near the midrange of its
anticipated service temperature range minimizes the risk
7.3—External reinforcement (encased and
exposed)
7.3.1 Description—External reinforcement may consist
of externally bonded fiber-reinforced polymer (FRP) materials, steel bars and strands, steel brackets, steel plates, steel
rolled sections or reinforced concrete jackets placed on the
outside of an existing concrete member. The new reinforcement is typically encased with concrete, shotcrete, mortar,
plaster, waterproofing or fireproofing, or it may be left
exposed and protected from corrosion with a coating; or
FRP, which is generally left exposed. Refer to ACI 440.2R
for more information regarding repair and strengthening
using FRP. Other types of reinforcement include deformed
steel bars, welded-wire reinforcement, steel rolled sections,
or specially fabricated brackets. ICRI 330.1 provides guidance on several strengthening methods, including externally
bonded systems, post-tensioning, section enlargement, and
supplemental supports.
Where members have been damaged by overload,
erosion, abrasion, or chemical attack, the deteriorated or
cracked concrete should be removed and new reinforcement
installed around and adjacent to the remaining concrete. In
these cases, the new reinforcement is encased in concrete,
trowel-applied mortar, or with shotcrete to replicate the original member profile or even to enlarge the size of the original
member to provide additional protective cover. Where the
existing concrete is in good condition, the new reinforcement may be bonded directly to the existing concrete surface
after preparing the surface as described in Chapter 3. Epoxy,
other chemical adhesives, or portland-cement concrete can
be used to bond the new reinforcement to the substrate,
or the reinforcement may be mechanically fastened to the
existing concrete.
7.3.2 Advantages and typical uses—Placement of external
reinforcement may be a more appropriate method for repair
and strengthening where obstructions limit access of equipment needed to remove existing concrete and to install
internal reinforcement. Additionally, if the concrete requires
repair and the placement of mortar, plaster, or shotcrete is
required for concrete rehabilitation, placement of external
reinforcement for strengthening may be accomplished in the
same construction process.
External flexural, shear, and torsion reinforcement for
concrete beams and girders may be provided by bonding
FRP sheets or strips to the member. Alternately, deformed
reinforcing bars or plates may be bonded to the surface of
the member with shotcrete, cast-in-place concrete, epoxy, or
polymer concrete. Anchors may be required in either repair
method to ensure composite action.
Steel plates may be attached to existing girders using
bolts, as illustrated in Fig. 7.3.2a.
Using a structural adhesive requires adequate surface preparation on both the steel and concrete, as well as selecting an
adhesive that is suitable to bond the steel to the concrete.
American Concrete Institute – Copyrighted © Material – www.concrete.org
58
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 7.3.2a—External reinforcement.
Fig. 7.3.2c—FRP reinforcement.
Fig. 7.3.2d—FRP reinforcement.
Fig. 7.3.2b—Column jacketing.
Abrasive blasting of both the steel plate and concrete surface
is an excellent preparation method, but surface cleaning by
other mechanical means or water blasting using a minimum
of 5000 psi (35 MPa) may be adequate.
Beams, girders, columns, and walls can be strengthened
by placing longitudinal reinforcing bars and stirrups or
ties around the members, and then encasing the members
with shotcrete or cast-in-place concrete (Fig. 7.3.2b).
The concrete bonds the new reinforcement to the existing
member. Because the added concrete increases the size of
the member and adds strength and stiffness, consideration
should be given to the additional weight of the member
resulting from such additions. Further, the added size of the
member increases the member’s stiffness, which may alter
the force distribution in the structure.
Both masonry and reinforced concrete walls have been
strengthened by adding layers of externally bonded FRP, or
by adding reinforcing bars or welded-wire reinforcement
to the face of the wall and using shotcrete to bond the new
reinforcement to the wall. Often, new dowels are embedded
in holes drilled into the wall to enhance the load transfer
between the existing wall and the reinforcement.
Beams, columns, and walls have also been strengthened
using FRP materials installed with bonding resin or mortar
(Fig. 7.3.2c). These systems should be designed in accordance with the recommendations of ACI 440.2R and the
manufacturer’s recommendations. Banding and strengthening with externally bonded FRP materials can be a costeffective method used to strengthen structural members
requiring seismic upgrade modifications (Fig. 7.3.2d).
Refer to ACI 440.2R. Strengthening with externally bonded
FRP materials is suitable for use where service loads are
increased, provided ductility is considered along with proper
provisions for fireproofing and waterproofing.
7.3.3 Limitations—Because the stiffness of most repaired
members is increased when plates or concrete encasement are
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
used, load distribution in the structure is altered and should
be analyzed. New overstresses may result at transitions
between strengthened and unstrengthened sections. Both
repaired and unrepaired members, including foundations,
should be checked for service load conditions. Strengthening with composite materials may provide the necessary
strengthening but, because of the brittle material behavior of
FRPs, the ultimate behavior of the FRP-strengthened system
should be carefully evaluated to ensure satisfactory performance. Refer to ACI 440.2R for guidance.
Surface preparation is critical if bonding is required for
composite action. Chapter 3 presents surface preparation
techniques.
Careful consideration should be exercised when using
structural adhesives, especially epoxy, due to their softening
and loss of strength at elevated temperatures near and above
their glass-transition temperature, which may be as low
as 120°F (50°C). Where required, appropriate fire protection should be provided. Proper detailing and protection is
especially critical when using FRP materials for strengthening because they are generally adhered to substrates with
epoxies. Some adhesives are moisture-sensitive and, when
applied to damp or moist surfaces, do not properly bond.
Bond tests should be conducted in accordance with ASTM
D7522. Pultruded FRP plates should be tested in accordance
with ASTM D3039, while FRP impregnated and wet laid-up
Fig. 7.4.1a—External post-tensioning of prestressed girder.
59
FRP should be tested in accordance with ASTM D7565.
ACI 440.8 material specifications provide test methods and
quality assurance guidelines for FRP.
7.4—External post-tensioning
7.4.1 Description—Girders and slabs may be strengthened in both flexure and shear by the addition of external
tendons, rods, or bolts that are tensioned after installation.
Figure 7.4.1a illustrates external post-tensioning examples; the external reinforcement may be straight or harped.
Figure 7.4.1b illustrates external reinforcement on a precast
concrete tee.
7.4.2 Advantages and typical uses—The use of highstrength prestressing steel reinforcement effectively reduces
the amount of reinforcement required for repair and strengthening. The prestressing may produce upward camber in
members, which helps to reduce service load deflection
while increasing both shear and flexural strength. Increased
shear resistance results from precompression of the concrete
member; and the flexural strength is increased due to the
addition of longitudinal reinforcement. The external posttensioning method is performed with the same equipment
and the same design criteria that all prestressing and posttensioning projects require. The end plates should be properly designed, securely seated, and sufficient space should
be provided for the equipment required to stress the strands
or rods. The post-tensioning force should be determined in
accordance with PCI, PTI, and ACI guidelines, including
PTI DC80.3-12/ICRI 320.6 (PTI/ICRI 2012).
7.4.3 Limitations—Placement and stressing of prestressing
strands and rods is often difficult in congested buildings and
interior locations. If proper positioning of stressing equipment is impossible or impractical, turnbuckles or nuts on
rods may be used to tension the steel, depending on the
forces required, but the tension in the steel is more difficult
to accurately measure using these methods.
Employing prestressing to close or reduce the size of
cracks may not be possible, as debris often collects in the
open crack. Cleaning and filling the crack with epoxy or other
appropriate material may be necessary before tensioning, in
order to have more effective load transfer across the plane
of the crack.
Fig. 7.4.1b—External post-tensioning of precast tee member prior to repair with shoring
in place (left), and after reinforcement is placed and encased at the center of the tee stem
(right).
American Concrete Institute – Copyrighted © Material – www.concrete.org
60
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 7.5.1—Collar around top of column – reinforcement in place (left) and after concrete
has been cast (right).
Providing adequate anchorage of the reinforcement is
important; however, this may be difficult to accomplish. Use
of steel grillages on the far side of columns and at the end
of beams, as shown in Fig. 7.4.1a, is advantageous because
such anchorage uses bearing forces and permits stressing
of the entire length of a member, including the end connections. Bolted or bonded side anchors are viable alternate
anchorages, but the anchors should be designed for the
resulting eccentric forces. Concrete members beyond the
anchor regions should be checked for strength and to assure
that restraint to post-tensioning deformations of the beam
section does not cause cracking between the end of the posttensioned section and the adjoining elements.
In indeterminate frames, post-tensioning induces
secondary moments and shear forces that should be considered when planning the repair. Also, the new, exposed
post-tensioned strands are visible and may be objectionable. Strands can be concealed in concrete or by cladding.
Building codes should be checked for requirements for the
installation of fireproofing on exposed reinforcement.
7.5—Jackets and collars
7.5.1 Description—Jacketing is a process where a section
of an existing structural member is increased in size by
encasement in concrete. A steel reinforcement cage is
constructed around the entire perimeter of the structurally
deficient section of a beam or column onto which shotcrete
or cast-in-place concrete is placed. Collars are jackets that
surround only a portion of the height of a column or pier and
typically are used to provide increased support to slabs or
beams. A shear collar is shown in Fig. 7.5.1.
A variety of materials, including conventional concrete
and mortar, epoxy mortar, grout, and latex-modified mortar
and concrete, have been used as encasement materials.
Techniques for filling the jacket include pumping, tremie, or
preplaced-aggregate concrete.
7.5.2 Advantages and typical uses—Jacketing is particularly applicable for the repair of deteriorated columns, piers
and piling where all or a portion of the section to be repaired
is under water. The method is applicable for protecting
concrete and steel sections against further deterioration and
for strengthening. Permanent forms are advantageous in
marine environments where added protection from weath-
ering, abrasion, and chemical pollution is desired. Collars
are effective in providing new capitals on existing columns
for supporting increased loads on floor slabs or beams. The
collar provides increased shear capacity for the slab, and
decreases the effective length of the column. Collars may
help satisfy architectural constraints better than jacketing the
column for its full height.
7.5.3 Limitations—Both jackets and collars require that all
deteriorated concrete be removed, structural cracks repaired,
existing reinforcement cleaned, and surfaces prepared. This
preparation is required so that the newly placed materials
properly bond with the existing structure. When jackets are
used under water, such preparation is expensive and difficult. The applicability of jackets and collars, however, is
widespread and cost-effective, especially if the alternative
is replacement of the structure supported by the deteriorated
member. For underwater conditions, a plastic shell may be
applied at the splash zone to help minimize abrasion of the
repair.
7.5.4 Installation details—The forming techniques used
and the decision to use permanent or temporary forms are
important details in jacketing. Timber or cardboard forms
may be used as temporary or permanent forms. Corrugated
steel forms are easy to assemble and are adequate temporary
or permanent forms. Permanent fiberglass, rubber, and fabric
forms have gained wide acceptance and some may provide
resistance to chemical attack after the repair is complete.
The jacket form is placed around the section to be repaired,
creating an annular void between the jacket and the surface
of the existing member. The form should be provided with
spacers to ensure equal clearance between it and the existing
member.
7.6—Supplemental members
7.6.1 Description—Supplemental members are new
columns, beams, braces, or infilled walls installed to permanently support damaged structural members or to support
additional loads, as illustrated in Fig. 7.6.1. The supplemental members are typically placed below the failed or
deflected areas to stabilize the structural framing.
7.6.2 Advantages and typical uses—Supplemental
members may be quickly installed and therefore are suitable temporary emergency repair solutions. Typically,
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
61
In Fig. 7.6.1(a), the new post supports a beam to increase
its flexural capacity. The new post requires adequate foundation support. As the single-span beam has become continuous with the addition of the post, the negative and positive moment regions should be assessed, considering that
adequate flexural reinforcement may not exist in critical
negative moment regions.
Figure 7.6.1(b) illustrates a post added to improve the
shear resistance and reduce the effective span of the existing
beam. Often, such posts added adjacent to an existing column
are more economical than collars. The post may be positioned eccentrically on the existing footing. If so, the footing
should be analyzed to determine if its size or strength needs
to be increased. In placing the post, a permanent jack, shims,
or both, may be required. The engineer should consider if
jacking effectively redistributes dead loads to the new posts.
Figure 7.6.1(c) illustrates placement of a supplemental
beam beneath an existing deflected slab. The space between
the new beam and existing structure should be shimmed or
dry-packed with grout. To provide lateral stability to the
supplemental member, it may be necessary to mechanically
anchor it to the existing slab. If the existing slab is supported
on beams, the new beam could be supported on the existing
beams instead of adding new posts.
Figures 7.6.4a and 7.6.4b are photographs of supplemental
members installed in place.
Special considerations for repair of structural
elements
Fig. 7.6.1—Supplemental members.
new members are installed to support seriously damaged,
cracked, or deflected flexural members. Often, the use of
supplemental members may be the most economical repair
alternative.
7.6.3 Limitations—Installing new columns or beams
may restrict space within the repaired column bay. A new
column obstructs passage and new beams reduce head room.
Aesthetically, the new beam or new column is noticeable
and may be distracting. The use of cross bracing, infilled
walls, or other means of providing resistance to lateral forces
may be needed to augment the structural capacity of the
original structure. Such bracing may further restrict interior
space utilization. Loads and stresses in the existing structure
may not be relieved by the supplemental members unless
special procedures such as jacking and/or shoring are used to
transfer loads; thus, these aspects should be considered. The
supplemental members may cause a redistribution of loads
and forces that overstresses nearby existing members, foundations, or both.
7.6.4 Installation details—New supplemental members
may be timber, steel, concrete, or masonry. The new
members should be tightly shimmed, wedged, or anchored
in position so that loads are transferred to the new members.
Care should be taken if lifting existing structural members
to avoid load-redistribution overstress of beams or adjacent
support members.
7.7—Repair of concrete columns
Repair procedures for concrete columns should consider
the compressive loads on the column(s) to be repaired.
Structural columns, by their nature, are designed to carry
vertical and sometimes lateral loads and bending moments.
Specifically, the self-weight of the structure plus the superimposed dead and live loads supported by the column during
the repair procedure should be considered when designing
concrete column repairs.
7.7.1 Concrete column repair categories—Repairs to
concrete columns typically fall into one of two categories:
1) surface or cosmetic repairs designed to address local deterioration; or 2) structural repairs that enhance or reestablish
the load-carrying capacity of the affected column(s).
When concrete columns require repair to address surface
deterioration, compressive loads have redistributed to the
unaffected portions of the column. In such instances, if the
deterioration does not significantly reduce the cross section,
conventional concrete repair procedures can successfully
address the damage without the need to unload the column
via shoring or jacking.
When column deterioration is extensive enough to affect
the load-carrying capacity of the column, then unloading
the column may be required such that, once the repair is
complete, the reintroduced loads are shared uniformly across
the entire cross section of the column. If it is not possible
to remove the load from the column, then a supplemental
column may provide an alternate load path to be used in
American Concrete Institute – Copyrighted © Material – www.concrete.org
62
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Fig. 7.6.4a—Supplemental members.
Fig. 7.6.4b—Supplemental members.
conjunction with the repair of the existing column, assuming
that the repair material does not undergo sufficient shrinkage
to cause a redistribution of the load or have insufficient bond
to the substrate to provide load transfer.
7.7.2 Column repair strategies—Column repair strategies
may vary with each condition but include:
a) Patching the column using repair materials compatible
with the original concrete;
b) Encasement or enlargement of the column cross section;
c) Confinement using steel plates or FRP materials;
d) Addition of shear collars to increase the shear capacity
of floor slabs and to decrease effective column length;
e) Addition of a steel plate assembly to increase moment
capacity;
f) Supplemental columns.
In addition to the aforementioned repair strategies, one
or more of the following protection strategies may be
employed, depending on the condition of the column:
a) The application of a chemical or barrier protection
system;
b) Cathodic protection;
c) Realkalization of the concrete adjacent to reinforcing
steel; or
d) Chloride extraction.
7.7.3 Column repair parameters
7.7.3.1 Unloading columns—Unless the column is
partially or fully unloaded by transferring the vertical load
above the repair to adjacent shoring before performing the
column repair, it is unlikely that the new repair will carry
any gravity load, particularly if the repair experiences any
drying shrinkage. It may be difficult and expensive to unload
columns, especially in tall buildings; however, the benefits
of unloading may outweigh costs if the structural repairs
are required to be fully effective. A properly constructed
repair will assist in resisting gravity loads and lateral loads;
however, the structural engineer should consider the effect
of significant deformation of the column prior to engagement of the repaired section, when shoring is not used to
unload prior to repair.
7.7.3.2 Redistribution of load—Redistribution of vertical
load has already occurred in the vicinity of the column
damage (due to corroded reinforcing steel, concrete cracking,
spalling, and/or delamination). The designer should account
for this in evaluating the remaining cross section to determine if the redistribution of load has overstressed the
column locally. The level of overstress may indicate a need
to at least partially relieve the column of load before the
repair operation.
7.7.3.3 Supplemental vertical reinforcing steel—Supplemental vertical column reinforcement should ideally be
placed within the existing column cage; however, this is
difficult to accomplish without cutting the column ties.
Cutting existing column ties may result in buckling loaded
vertical reinforcement; therefore, it is typically prudent to
place additional reinforcing steel bars outside the existing
ties, installing additional new ties to provide confinement of
the new vertical reinforcing bars.
7.7.3.4 Concrete removal—Removal of concrete within
a column cage, inside the vertical reinforcement and ties,
especially over a significant portion of the height of the
vertical reinforcing bars, is a major concern. When too much
concrete is removed from inside the cage, the vertical bars
could buckle, even if the column ties are left intact. In addition, the removal of any concrete in a loaded column during
the repair process may cause even further load redistribution
across the remaining concrete and reinforcing bars. Analysis
should define the limit of such concrete removal to prevent a
compression failure of the column.
7.7.3.5 Corroded reinforcing steel—Typically, it is unnecessary to remove corroded reinforcing bars where reduced
cross-sectional area occurs, even when additional reinforcing bars are installed to replace the lost cross-sectional
area. Proper lap lengths for the added reinforcing bar should
be provided above and below the corroded portion of the
reinforcing bar. If adequate length for lap splicing cannot
be accomplished, the existing bars may be welded to a
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
supplemental bar or to a steel plate or angle to join sections
of existing reinforcement to effectively transfer load. Welds
should be made according to American Welding Society (AWS
D1.4), with due consideration to requirements of preheating
and the effects to surrounding concrete from such preheating
and welding. Any corroded reinforcement that is left in place
should be thoroughly cleaned by sandblasting, to bare metal if
possible, to reduce the likelihood of future corrosion.
7.7.3.6 Supplemental reinforcing steel—When the supplemental vertical reinforcing bars are placed outside the
existing ties, the column dimensions should be increased
to provide adequate cover. Hairpin ties are often added to
laterally support the supplemental vertical bars. The hairpin
ties may be epoxy bonded into holes drilled into the existing
column in accordance with Appendix D of ACI 318.
7.7.3.7 Corroded ties—When column deterioration results
from corroded ties, it is important that repairs include appropriate measures to laterally confine the vertical bars. This
can be accomplished by adding hairpin ties anchored into
the concrete. It is often necessary to build out the column
concrete to provide adequate cover over the supplemental
ties. Potential buckling problems in the vertical bars may be
avoided with this technique.
7.7.3.8 Low-strength concrete—Where low concrete
strength results in insufficient load-carrying capacity, several
alternatives are available:
a) Shore the column and remove and replace the lowstrength concrete with repair concrete to match the required
strength of the column;
b) Shore the column and increase the size of the column
using additional vertical bars, ties, and concrete with strength
compatible with the low-strength concrete in the column,
thereby increasing the area of the column and increasing its
load capacity;
c) Wrap the column with externally bonded FRP materials
to provide confinement such that the strength of the confined
material is equivalent to that required;
d) Install a supplemental column.
7.8—Repair of concrete beams, girders, and joists
Similar to concrete columns, repair procedures for concrete
beams, girders, and joists must consider the existing structural loads on the members to be repaired. Concrete beams,
girders, and joists are normally designed to carry shear loads
and bending moments. The self-weight of the structure
plus any superimposed dead and live loads that cannot be
removed before repair should be considered when designing
repairs for concrete beams, girders, and joists.
7.8.1 Concrete beam, girder, and joist repair categories—
Repairs typically fall into one of two categories: 1) surface
or cosmetic repairs designed to address local deterioration;
or 2) structural repairs that enhance or reestablish the loadcarrying capacity of the affected members.
When concrete beams, girders, or joists require repair due
to surface deterioration, structural loads may be less critical,
given that loads have redistributed to the undisturbed cross
section of the member. If the deterioration does not signifi-
63
cantly reduce the cross section, conventional concrete repair
procedures can successfully address the damage.
When deterioration of the member is significant, then
unloading the member may be required such that once the
repair is complete, the entire cross section of the beam, girder,
or joist carries the reintroduced loads. If it is not possible to
remove all loads from the member, then the repair concrete
and any added reinforcement will only carry loads added
after the repair is completed. The area of concrete and original reinforcement, reduced to account for any deterioration,
should be checked to confirm that the unrepaired section is
capable of carrying all dead and live loads superimposed
on the member after the repair is completed. Repair design
should also consider the capacity of the unrepaired section to
carry required dead and live loads during repair.
7.8.2 Repair strategies—Beam, girder, and joist repair
strategies may vary with each condition but include:
a) Patching the member using repair materials compatible
with the original concrete
b) Adding additional mild steel reinforcement, often
accompanied by enlargement of the member cross section;
c) Supplemental exterior reinforcement using steel plates,
or FRP materials;
d) External prestressing, and
e) Supplemental columns to reduce the span of the affected
member.
In addition to the aforementioned repair strategies, one or
more of the following protection strategies may be employed,
depending on the condition of the beam, girder, or joist:
a) The application of a chemical or barrier protection
system;
b) Cathodic protection;
c) Realkalization of the concrete adjacent to reinforcing
steel;
d) Chloride extraction.
7.8.3 Repair parameters
7.8.3.1 Unloading beams, girders, and joists—Unless the
member is unloaded by transferring some or all existing loads
by shoring and jacking before performing the repair, it is
unlikely that the new repair will carry any load, except those
loads that are applied after the repairs are completed, particularly if the repair experiences any drying shrinkage. If the
member cannot be unloaded, the repair should be designed
considering that the original portion of the member’s net
cross-sectional area is reduced to account for deterioration
of the concrete and reduced areas of reinforcing steel due to
corrosion. The analysis should also consider all dead loads
and live loads in place at the time of repair, and the portion
of superimposed dead and live loads carried by the original,
unrepaired member.
7.8.3.2 Preloading simple span prestressed beams,
girders, and joists—Repairs made to the precompressed
tension zone, bottom-of-the-center section, of simple span
prestressed beams, girders, and joists, including doubletees, are likely to crack prematurely if the members are not
preloaded before repair. The preload should be calculated
such that, with the preload force and dead loads on the
member at the time of repair, the precompression load in the
American Concrete Institute – Copyrighted © Material – www.concrete.org
64
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
repair area is eliminated. This will allow the repair concrete
to be compressed to the same level as the surrounding
concrete once the preload is removed. If this is not done,
the tension stress under full design load will be significantly
higher in the repair concrete than in the original concrete
surrounding the repair.
7.8.3.3 Redistribution of the load—Redistribution of shear
and bending forces has already occurred in the vicinity of the
corroded reinforcing steel and resulting delamination. The
designer should be aware of this and carefully evaluate the
remaining cross section to determine if the redistribution of
load has overstressed the member locally. If so, it may be
necessary to at least partially relieve the member of load via
shoring and jacking before the repair operation.
7.8.3.4 Concrete removal—The removal of concrete in a
compression zone or in areas with high shear forces should
be analyzed to establish the limit of concrete removal to
avoid potential overstress and sudden failure.
7.8.3.5 Corroded reinforcing steel—Typically, it is unnecessary to remove corroded reinforcing bars with reduced
cross-sectional area if additional reinforcing bars are added
to replace the lost cross-sectional area. Any corroded reinforcement that is left in place should be thoroughly cleaned
by abrasive blasting, to bare metal if possible to reduce the
likelihood of future corrosion. Proper lap splice lengths for
the added reinforcing bar should be provided on each end
of the corroded portion of the reinforcing bar that is supplemented. If adequate length for lap splicing cannot be accomplished, the existing bars may be mechanically coupled or
welded to a supplemental bar or to a steel plate or angle to
effectively join sections of existing reinforcement to develop
their required strength. The welds should be made according
to AWS D1.4 with careful consideration to requirements of
preheating and the effects to surrounding concrete from such
preheating and welding.
7.9—Repair of concrete structural slabs
Considerations for repair of concrete structural slabs are
similar to those for beams, girders, and joists, with the additional consideration of punching shear. If repairs are made
to a flat slab or flat plate system in the vicinity of a column,
punching shear stresses should be considered and shoring
of the slab may be required. Like concrete beams, consideration should be given to the existing loads on the slab at
the location of the repair; however, unlike beams, significant redistribution of the load is possible and may likely
have already occurred. Especially when large repair areas
are anticipated in slabs, shoring should be considered not
only in the vicinity of the slab repair, but also extending to
adjacent bays.
7.9.1 Concrete structural slab repair categories—Repairs
typically fall into one of two categories: 1) surface or
cosmetic repairs designed to address local deterioration;
or 2) structural repairs that enhance or reestablish the loadcarrying capacity of the slab.
When concrete slabs require repair due to surface deterioration, structural loads are redistributed to the undamaged
portion of the slab. If the deterioration does not significantly
reduce the cross section, conventional concrete repair procedures can successfully address the damage.
When deterioration of the slab is significant, then
unloading the slab may be required so that once the repair
is complete, the entire slab will carry the reintroduced loads.
If it is not possible to remove the load from the slab, then
the repair concrete and any added reinforcement will carry
only loads added after the repair is completed. The area of
concrete and original reinforcement, reduced to account for
any deterioration, should be checked to confirm that it is
capable of carrying all dead and live loads on the slab at
the time of repair, in addition to its proportional share of all
dead and live loads superimposed on the slab after the repair
is completed.
7.9.2 Repair strategies—Structural slab repair strategies
may vary with each condition but include:
a) Patching the member using repair materials compatible with the original concrete; shotcrete is often used on the
underside of slabs for this purpose;
b) Adding additional mild steel reinforcement, often
accompanied by enlargement of the member cross section
when installed on the bottom of the slab, and often cut into
the slab and bonded with epoxy when installed on the top of
the slab;
c) Supplemental exterior reinforcement using steel plates
or FRP materials;
d) Addition of collars or brackets below the slab to
increase the punching shear perimeter and, thus, increase the
shear capacity of the slab.
In addition to the above repair strategies, one or more
of the following protection strategies may be employed,
depending on the condition of the slab:
a) The application of a chemical or barrier protection
system;
b) Cathodic protection;
c) Realkalization of the concrete adjacent to reinforcing
steel;
d) Chloride extraction.
7.9.3 Repair parameters
7.9.3.1 Unloading structural slabs—Unless the slab is
unloaded by transferring all existing loads to shoring before
performing the repair, it is unlikely that the new repair will
carry any load, except those loads that are applied after the
repairs are completed, particularly if the repair exhibits any
drying shrinkage. If the slab cannot be unloaded, the repair
must be carefully designed. The portion of the remaining slab
should be checked using net cross-sectional area of concrete
accounting for deterioration of the concrete and reduced
areas of reinforcing steel due to corrosion, and before any
supplemental reinforcement or patching concrete is added.
The check should account for all dead loads, live loads in
place at the time of repair, and its portion of superimposed
dead and live loads.
7.9.3.2 Load redistribution—Redistribution of shear and
bending forces has already occurred in the vicinity of the
corroded reinforcing steel and resulting delamination. The
designer should be aware of this and carefully evaluate
the remaining cross section to determine if the redistribu-
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
tion of load has overstressed the member locally. If so, it
might be necessary to at least partially relieve the member
of load before the repair operation. In addition, the designer
should carefully consider the redistribution of load whenever repairs are made to cantilevered slabs, either on the
cantilever itself or on the backspan. Shoring is often required
when performing repairs on cantilevered slabs.
7.9.3.3 Concrete removal—The removal of concrete in
a compression zone or in areas with high shear forces is a
major concern. When too much concrete is removed from
a compression or high shear zone, the remaining concrete
could become overstressed and fail, often suddenly. The
designer of the repair should carefully consider the amount
of concrete that will be removed, any prestress forces that
may exist, and the amount of corroded reinforcement that is
lost, when determining the need for shoring.
7.9.3.4 Corroded reinforcing steel—Cutting through
existing corroded reinforcement that is under stress will
result in redistribution of stress, transferring loads to other
parts of the structure. Because of this, it is generally not
advisable to remove corroded reinforcing bars with reduced
cross-sectional area even if additional reinforcing bars are
added to replace the lost cross-sectional area. An exception is
when shoring and jacking has been installed so as to unload
the member and reinforcement. Proper lap lengths for the
added reinforcing bar should be provided on each side of the
corroded portion of the reinforcing bar that is supplemented.
The supplemental bar(s) should be spliced to the deteriorated portion of the corroded reinforcement to replace the
lost cross-sectional area. If adequate length for lap splicing
cannot be accomplished, the existing bars may be mechanically spliced or welded to a supplemental bar or to a steel
plate or angle to join sections of existing reinforcement. The
welds should be made according to AWS D1.4 with careful
consideration to requirements of preheating and the effects
to surrounding concrete from such preheating and welding.
Any corroded reinforcement that is left in place should be
thoroughly cleaned by abrasive blasting, to bare metal if
possible, to reduce the likelihood of future corrosion.
CHAPTER 8—REFERENCES
AASHTO
M-235-03 (2012)—Standard Specification for Epoxy
Resin Adhesives
T 259-02 (2012)—Standard Method of Test for Resistance
of Concrete to Chloride Ion Penetration
T 260 -97 (2011)—Standard Method of Test for Sampling
and Testing for Chloride Ion in Concrete and Concrete Raw
Materials
American Concrete Institute
201.1R-08—Guide for Conducting a Visual Inspection of
Concrete in Service
201.2R-08—Guide to Durable Concrete
207.3R-94(08)—Practices for Evaluation of Concrete in
Existing Massive Structures for Service Conditions
65
210R-93(08)—Erosion of Concrete in Hydraulic
Structures
210.1R-94—Compendium of Case Histories on Repair
of Erosion-Damaged Concrete in Hydraulic Structures
(withdrawn)
211.1-91(09)—Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete
212.3R-10—Report on Chemical Admixtures for Concrete
222R-01(10)—Protection of Metals in Concrete against
Corrosion
222.3R-11—Guide to Design and Construction Practices to Mitigate Corrosion of Reinforcement in Concrete
Structures
223R-10—Guide for the Use of Shrinkage-Compensating
Concrete
224.1R-07—Causes, Evaluation, and Repair of Cracks in
Concrete Structures
224.3R-95(13)—Joints in Concrete Construction
228.2R-13—Report on Nondestructive Test Methods for
Evaluation of Concrete in Structures
232.1R-12—Report on the Use of Raw or Processed
Natural Pozzolans in Concrete
232.2R-03—Use of Fly Ash in Concrete
234R-06—Guide for the Use of Silica Fume in Concrete
237R-07—Self-Consolidating Concrete
301-10—Specifications for Structural Concrete
302.2R-06—Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials
304R-00(09)—Guide for Measuring, Mixing, Transporting, and Placing Concrete
304.1R-92—Guide for the Use of Preplaced Aggregate
Concrete for Structural and Mass Concrete Applications
(withdrawn)
304.2R-96(08)—Placing Concrete by Pumping Methods
304.5R-91(97)—Batching, Mixing, and Job Control of
Lightweight Concrete (withdrawn)
304.6R-09—Guide for Use of Volumetric-Measuring and
Continuous-Mixing Concrete Equipment
305R-10—Guide to Hot Weather Concreting
306R-10—Guide to Cold Weather Concreting
306.1-90(02)—Standard Specification for Cold Weather
Concreting
308.1-11—Specification for Curing Concrete
308R-01(08)—Guide to Curing Concrete
309R-05—Guide for Consolidation of Concrete
311.1R-07—ACI Manual of Concrete Inspection (SP-2)
(Synopsis)
311.4R-05—Guide for Concrete Inspection
311.5-04—Guide for Concrete Plant Inspection and
Testing of Ready-Mixed Concrete
318-11—Building Code Requirements for Structural
Concrete and Commentary
345R-11—Guide for Concrete Highway Bridge Deck
Construction
350.1-10—Specification for Tightness Testing of Environmental Engineering Concrete Structures and Commentary
355.1R-91—Report on Anchorage to Concrete
(withdrawn)
American Concrete Institute – Copyrighted © Material – www.concrete.org
66
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
355.2-07—Qualification of Post-Installed Mechanical
Anchors in Concrete and Commentary
362.1R-12—Guide for the Design of Durable Concrete
Parking Structures
362.2R-00(13)—Guide for Structural Maintenance of
Parking Structures
364.1R-07—Guide for Evaluation of Concrete Structures
before Rehabilitation
364.3R-09—Guide for Cementitious Repair Material
Data Sheet
423.4R-98—Corrosion and Repair of Unbonded Single
Strand Tendons
423.8R-10—Report on Corrosion and Repair of Grouted
Multistrand and Bar Tendon Systems
437R-03—Strength Evaluation of Existing Concrete
Buildings
439.3R-07—Types of Mechanical Splices for Reinforcing
Bars
440R-07—Report on Fiber-Reinforced Polymer (FRP)
Reinforcement for Concrete Structures
440.1R-06—Guide for the Design and Construction of
Structural Concrete Reinforced with FRP Bars
440.2R-08—Guide for the Design and Construction of
Externally Bonded FRP Systems for Strengthening Concrete
Structures
440.3R-12—Guide Test Methods for Fiber-Reinforced
Polymers (FRP) Composites for Reinforcing or Strengthening Concrete and Masonry Structures
440.8-13—Specification for Carbon and Glass Fiber-Reinforced Polymer (FRP) Materials Made by Wet Layup for
External Strengthening of Concrete and Masonry Structures
503R-93—Use of Epoxy Compounds with Concrete
(withdrawn)
503.4-92(03)—Specifications for Repairing Concrete
with Epoxy Mortars
503.6R-91—Guide for the Application of Epoxy and
Latex Adhesives for Bonding Freshly Mixed and Hardened
Concretes (withdrawn)
503.7-07—Specification for Crack Repair by Epoxy
Injection
504R-90—Guide to Joint Sealants for Concrete Structures
(withdrawn)
506R-05—Guide to Shotcrete
506.1R-08—Guide to Fiber-Reinforced Shotcrete
506.3R-91—Guide to Certification of Shotcrete
Nozzlemen (withdrawn)
515.1R-85—Guide to the Use of Waterproofing, Dampproofing, Protective, and Decorative Barrier Systems for
Concrete (withdrawn)
515.2R-13—Guide to Selecting Protective Treatments for
Concrete
544.1R-96(09)—Report on Fiber Reinforced Concrete
544.3R-08—Guide for Specifying, Proportioning, and
Production of Steel Fiber-Reinforced Concrete
544.4R-88(09)—Design Considerations for Steel Fiber
Reinforced Concrete
546.1R-80—Guide for Repair of Concrete Bridge Superstructures (withdrawn)
546.2R-10—Guide to Underwater Repair of Concrete
546.3R-14—Guide for the Selection of Materials for the
Repair of Concrete
548.1R-09—Guide for the Use of Polymers in Concrete
548.2R-93—Guide for Mixing and Placing Sulfur
Concrete in Construction (withdrawn)
548.3R-09—Report on Polymer Modified Concrete
548.4-11—Specification for Latex-Modified Concrete
(LMC) Overlays
548.5R-94(98)—Guide for Polymer Concrete Overlays
548.8-07—Specification for Type EM (Epoxy Multi-Layer)
Polymer Overlay for Bridge and Parking Garage Decks
548.10-10—Specification for Type MMS (Methyl Methacrylate Slurry) Polymer Overlays for Bridge and Parking
Garage Decks
562-13—Code Requirements for Evaluation, Repair, and
Rehabilitation of Concrete Buildings and Commentary
RAP-1-03(09)—Structural Crack Repair by Epoxy Injection
RAP-2-03(09)—Crack Repair by Gravity Feed with Resin
RAP-3-03(09)—Spall Repair by Low-Pressure Spraying
RAP-4-03(09)—Surface Repair Using Form-and-Pour
Techniques
RAP-5-03(09)—Surface Repair Using Form-and-Pump
Techniques
RAP-6-03(09)—Vertical and Overhead Spall Repair by
Hand Application
RAP-7-05(10)—Spall Repair of Horizontal Concrete
Surfaces
RAP-8-05(10)—Installation of Embedded Galvanic
Anodes
RAP-9-05(10)—Spall Repair by the Preplaced Aggregate
Method
RAP-12-10—Concrete Repair by Shotcrete Application
RAP-13-10—Methacrylate Flood Coat
RAP-14-10—Concrete Removal Using Hydrodemolition
ASTM International
A185-79—Standard Specification for Welded Steel Wire
Fabric for Concrete Reinforcement
A497-79—Standard Specification for Welded Deformed
Steel Wire Fabric for Concrete Reinforcement
A615/A615M-07—Standard Specification for Deformed
and Plain Carbon Steel Bars for Concrete Reinforcement
A616/A616M-96a—Standard Specification for Rail Steel
Deformed and Plain Bars for Concrete Reinforcement (withdrawn 1999)
A617/A617M-96a—Standard Specification for AxleSteel Deformed and Plain Bars for Concrete Reinforcement
(withdrawn 1999)
A706/A706M-01—Standard Specification for Low-Alloy
Steel Deformed and Plain Bars for Concrete Reinforcement
A767/A767M-09—Standard Specification for ZincCoated (Galvanized) Steel Bars for Concrete Reinforcement
A775/A775M-07b(2014)—Standard Specification for
Epoxy-Coated Steel Reinforcing Bars
A780/780M-09—Standard Practice for Repair of
Damaged and Uncoated Areas of Hot-Dip Galvanized
Coatings
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
B117-90—Standard Test Method of Salt Spray (Fog)
Apparatus
C67-13a—Standard Test Methods of Sampling and
Testing Brick and Structural Clay Tile
C94/C94M-14—Standard Specification for Ready-Mixed
Concrete
C125-13b—Standard Terminology Relating to Concrete
and Concrete Aggregates
C157/C157M-08—Standard Test Method for Length
Change of Hardened Hydraulic-Cement Mortar and Concrete
C267-01(2012)—Standard Test Methods for Chemical
Resistance of Mortars, Grouts, and Monolithic Surfacings
and Polymer Concretes
C293/C293M-10—Standard Test Method for Flexural
Strength of Concrete (Using Simple Beam with Center-Point
Loading)
C387-04—Standard Specification for Packaged, Dry,
Combined Materials for Mortar and Concrete
C469/C469M-14—Standard Test Method for Static
Modulus of Elasticity and Poisson’s Ratio of Concrete in
Compression
C494/C494M-13—Standard Specification for Chemical
Admixtures for Concrete
C496/C496M-11—Standard Test Method for Splitting
Tensile Strength of Cylindrical Concrete Specimens
C531-00—Standard Test Method for Linear Shrinkage
and Coefficient of Thermal Expansion of Chemical-Resistant Mortars, Grouts, Monolithic Surfacings, and Polymer
Concretes
C597-09—Standard Test Method for Pulse Velocity
through Concrete
C642-13—Standard Test Method for Density, Absorption,
and Voids in Hardened Concrete
C672/C672M-12—Standard Test Method for Scaling
Resistance of Concrete Surfaces Exposed to Deicing
Chemicals
C685/C685M-11—Standard Specification for Concrete
Made by Volumetric Batching and Continuous Mixing
C806-12—Standard Test Method for Restrained Expansion of Expansive Cement Mortar
C836/C836M-12—Standard Specification for High Solids
Content, Cold Liquid-Applied Elastomeric Waterproofing
Membrane for Use with Separate Wearing Course
C845/C845M-12—Standard Specification for Expansive
Hydraulic Cement
C878/C878M-14—Standard Test Method for Restrained
Expansion of Shrinkage-Compensating Concrete
C881/C881M-13—Standard Specification for EpoxyResin-Base Bonding Systems for Concrete
C882/C882M-13a—Standard Test Method for Bond
Strength of Epoxy-Resin Systems Used with Concrete by
Slant Shear
C900-13a—Standard Test Method for Pullout Strength of
Hardened Concrete
C920-14—Standard Specification for Elastomeric Joint
Sealants
67
C928/C928M-13—Standard Specification for Packaged,
Dry, Rapid-Hardening Cementitious Materials for Concrete
Repairs
C1059/C1059M-13—Standard Specification for Latex
Agents for Bonding Fresh to Hardened Concrete
C1107/C1107M-13—Standard Specification for Packaged Dry Hydraulic-Cement Grout (Nonshrink)
C1116/C1116M-03—Standard Specification for FiberReinforced Concrete and Shotcrete
C1152/C1152M-04(2012)e1—Standard Test Method for
Acid-Soluble Chloride in Mortar and Concrete
C1218/C1218M-99(2008)—Standard Test Method for
Water-Soluble Chloride in Mortar and Concrete
C1240-10—Standard Specification for Silica Fume Used
in Cementitious Mixtures
C1383-04(2010)—Standard Test Method for Measuring
the P-Wave Speed and the Thickness of Concrete Plates
Using the Impact-Echo Method
C1438-13—Standard Specification for Latex and Powder
Polymer Modifiers for use in Hydraulic Cement Concrete
and Mortar
C1439-13—Standard Test Methods for Evaluating Latex
and Powder Polymer Modifiers for use in Hydraulic Cement,
Concrete, and Mortar
C1582/C1582M-11—Standard Specification for Admixtures to Inhibit Chloride-Induced Corrosion of Reinforcing
Steel in Concrete
C1583/C1583M-13—Standard Test Method for Tensile
Strength of Concrete Surfaces and the Bond Strength or
Tensile Strength of Concrete Repair and Overlay Materials
by Direct Tension (Pull-off Method)
C1600/C1600M-11—Standard Specification for Rapid
Hardening Hydraulic Cement
D56-05(2010)—Standard Test Method for Flash Point by
Tag Closed Cup Tester
D93-13e1—Standard Test Methods for Flash Point by
Pensky-Martens Closed Cup Tester
D98-05(2013)—Standard Specification for Calcium
Chloride
D333-01(2013)—Standard Guide for Clear and Pigmented
Lacquers
D412-06a(2013)—Standard Test Methods for Vulcanized
Rubber and Thermoplastic Rubbers and Thermoplastic Elastomers – Tension
D429-14—Standard Test Method for Rubber Property—
Adhesion to Rigid Substrates
D522/D522M-13—Standard Test Methods for Mandrel
Bend Test of Attached Organic Coatings
D638-10—Standard Test Method for Tensile Properties of
Plastics
D695-10—Standard Test Method for Compressive Properties of Rigid Plastics
D1353-13—Standard Test Method for Nonvolatile Matter
in Volatile Solvents for Use in Paint, Varnish, Lacquer, and
Related Products
D1471-69—Method of Test for Two-Parameter 60 Deg
Specular Gloss (withdrawn 1975)
American Concrete Institute – Copyrighted © Material – www.concrete.org
68
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
D1623-09—Standard Test Method for Tensile and Tensile
Adhesion Properties of Rigid Cellular Plastics
D1640-03(2009)—Standard Test Methods for Drying,
Curing, or Film Formation of Organic Coatings at Room
Temperature
D1647-89(1996)e1—Standard Test Methods for Resistance of Dried Films of Varnishes to Water and Alkali (withdrawn 2004)
D1653-13—Standard Test Methods for Water Vapor
Transmission of Organic Coating Films
D2047-11—Standard Test Method for Static Coefficient
of Friction of Polish-Coated Floor Surfaces as Measured by
the James Machine
D2134-93(2012)—Standard Test Method for Determining
the Hardness of Organic Coatings with a Sward-Type Hardness Rocker
D2196-10—Standard Test Methods for Rheological Properties of Non-Newtonian Materials by Rotational (Brookfield type) Viscometer
D2197-13—Standard Test Method for Adhesion of
Organic Coatings by Scrape Adhesion
D2240-05(2010)—Standard Test Method for Rubber
Property-Durometer Hardness
D2247-11—Standard Practice for Testing Water Resistance of Coatings in 100% Relative Humidity
D2370-98(2010)—Standard Test Method for Tensile
Properties of Organic Coatings
D2565-99(2008)—Standard Practice for Xenon-Arc
Exposure of Plastics Intended for Outdoor Applications
D2794-93(2010)—Standard Test Method for Resistance
of Organic Coatings to the Effects of Rapid Deformation
(Impact)
D3039/3039M-14—Standard Test Method for Tensile
Properties of Polymer Matrix Composite Materials
D3278-96(2011)—Standard Test Method for Flash Point
of Liquids by Small Scale Closed-Cup Apparatus
D3359-09e2—Standard Test Methods for Measuring
Adhesion by Tape Test
D3363-05(2011)e2—Standard Test Method for Film Hardness by Pencil Test
D4141/D4141M-14—Standard Practice for Conducting
Black Box and Solar Concentrating Exposures of Coatings
D4214-98—Standard Test Methods for Evaluating Degree
of Chalking of Exterior Paint Films (withdrawn 2007)
D4258-05(2012)—Standard Practice for Surface Cleaning
Concrete for Coating
D4259-88(2012)—Standard Practice for Abrading
Concrete
D4260-05(2012)—Standard Practice for Liquid and
Gelled Acid Etching Concrete
D4262-05(2012)—Standard Test Method for pH of
Chemically Cleaned or Etched Concrete Surfaces
D4417-14—Standard Test Methods for Field Measurement of Surface Profile of Blast Cleaned Steel
D4541-09e1—Standard Test Method for Pull-Off Strength
of Coatings Using Portable Adhesion Testers
D4580/4580M-12—Standard Practice for Measuring
Delaminations in Concrete Bridge Decks by Sounding
D4788-03(2013)—Standard Test Method for Detecting
Delaminations in Bridge Decks Using Infrared Thermography
D6087-08—Standard Test Method for Evaluating
Asphalt–Covered Concrete Bridge Decks Using Ground
Penetrating Radar
D7522/7522M-09—Standard Test Method for Pull-Off
Strength for FRP Bonded to Concrete Substrate
D7565/7565M-10—Standard Test Method for Determining Tensile Properties of Fiber Reinforced Polymer
Matrix Composites Used for Strengthening Civil Structures
D7682-12—Standard Test Method for Replication and
Measurement of Concrete Surface Profiles Using Replica Putty
E96/E96M-13—Standard Test Methods for Water Vapor
Transmission of Materials
E329-14—Standard Specification for Agencies Engages
in Construction Inspection, Testing, or Special Inspection
E514/514M-14—Standard Test Method for Water Penetration and Leakage Through Masonry
E965-96(2006)—Standard Test Method for Measuring
Pavement Macrotexture Depth Using a Volumetric Technique
E1216-11—Standard Practice for Sampling for Particulate Contamination by Tape Lift
F710-11—Standard Practice for Preparing Concrete
Floors to Receive Resilient Flooring
G109-07(2013)—Standard Test Method for Determining
Effects of Chemical Admixtures on Corrosion of Embedded
Steel Reinforcement in Concrete Exposed to Chloride
Environments
American Welding Society (AWS)
D1.4:2005—Structural Welding Code—Reinforcing Steel
Federal Specifications
TT-C-555B-75—Coating, Textured (For Interior and
Exterior Masonry Surfaces)
TT-P-1411A-73—Paint, Copolymer-Resins Cementitious
(For Waterproofing Concrete and Masonry Walls)
TT-S-001543A-71—Interim
Federal
Specification,
Sealing Compound: Silicone Rubber Base (For Calking,
Sealing, and Glazing in Buildings and Other Structures
TT-S-00227E-69—Interim Federal Specification, Sealing
Compound: Elastomeric Type, Multi-Component (For
Calking, Sealing, and Glazing in Buildings and Other
Structures)
TT-S-00230C-70—Interim Federal Specification, Sealing
Compound: Elastomeric Type, Single Component (For Calking,
Sealing, and Glazing in Buildings and Other Structures)
International Code Council—Evaluation Service (ICC-ES)
AC125-12—Acceptance Criteria for Concrete and Reinforced and Unreinforced Masonry Strengthening Using
Externally Bonded Fiber-Reinforced Polymer (FRP)
Composite Systems
International Concrete Repair Institute (ICRI)
120.1-09—Guidelines and Recommendations for Safety
in the Concrete Repair Industry
American Concrete Institute – Copyrighted © Material – www.concrete.org
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
130.1R-09—Guide for Methods of Measurement and
Contract Types for Concrete Repair Work
210.1-98—Guide for Verifying Field Performance of
Epoxy Injection of Concrete Cracks
210.3-04—Guide for Using In-Situ Tensile Pull-off Tests
to Evaluate Bond of Concrete Surface Materials
210.4-09—Guide for Nondestructive Evaluation Methods
for Condition Assessment, Repair, and Performance Monitoring of Concrete Structures
310.1R-08—Guide for Surface Preparation for the Repair
of Deteriorated Concrete Resulting from Reinforcing Steel
Corrosion
310.2R-13—Selecting and Specifying Concrete Surface
Preparation for Sealers, Coatings, and Polymer Overlays,
and Concrete Repair
310.3-04—Guide for the Preparation of Concrete Surfaces
for Repair Using Hydrodemolition Methods
320.2R-09—Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces
320.3R-12—Guide for Inorganic Repair Material Data
Sheet Protocol
330.1-06—Guideline for the Selection of Strengthening
Systems for Concrete Structures
340.1-06—Guideline for Selecting Grouts to Control
Leakage in Concrete Structures
NACE International
01101—Electrochemical Chloride Extraction from SteelReinforced Concrete—A State-of-the-Art Report
01102—State-of-the-Art Report: Criteria for Cathodic
Protection of Prestressed Concrete Structures
01104—Electrochemical Realkalization of Steel-Reinforced Concrete—A State-of-the-Art Report
01105—Sacrificial Cathodic Protection of Reinforced
Concrete Elements—A State-of-the-Art Report
National Science Foundation (NSF)
NSF/ANSI 61-07—Drinking Water System Components—Health Effects
RILEM
II.4-87—Water Absorption Under Low Pressure (Pipe
Method)
The Society for Protective Coating (SSPC)
PA 7—Applying Thin Film Coatings to Concrete
SSPC-Paint 38—Single Component Moisture—Cure
Weatherable, A
SSPC-SP13/NACE 6—Surface Preparation of Concrete
TR 5—Preparation of Protective Coating Specifications
for Atmospheric Service
TU 2—Design, Installation, and Maintenance of Coating
Systems for Concrete Used in Secondary Containment
TU 10—Procedures for Applying Thick Film Coatings and
Surfacings Over Concrete Floors
Transportation Research Board (TRB)/Strategic Highway
Research Program (SHRP)
69
SHRP-S-336—Techniques for Concrete Removal and Bar
Cleaning on Bridge Rehabilitation Projects
SHRP-S-337—Cathodic Protection of Reinforced
Concrete Bridge Elements: A State-of-the-Art Report
Authored documents
Al-Fadhala, M., and Hover, K. C., 2001, “Rapid Evaporation from Freshly Cast Concrete and the Gulf Environment,”
Construction & Building Materials, V. 15, No. 1, Jan., pp.
1-7. doi: 10.1016/S0950-0618(00)00064-7
Al-Qadi, I. L.; Prowell, B. D.; Weyers, R. E.; Dutta, T.;
Gouru, H.; and Berke, N., 1992, “Corrosion Inhibitors and
Polymers,” Report No. SHRP-S-666, Strategic Highway
Research Program, National Research Council, Washington,
DC.
Berke, N. S.; Dallaire, M. P.; Weyers, R. E.; Henry, M.
B.; Peterson, J. E.; and Powell, B., 1992, “Impregnation
of Concrete Corrosion Inhibitors,” Corrosion Forms and
Control for Infrastructure, ASTM STP 1137, V. Chaker, ed.,
ASTM International, West Conshohocken, PA, 432 pp.
Best, J., and McDonald, J., 1990, “Evaluation of Polyester
Resin, Epoxy and Cement Grouts for Embedding Reinforcing Steel Bars in Hardened Concrete,” Technical Report
REMR-CS-23, USACE, Vicksburg, MS, Apr., 69 pp.
Elsner, B., 2000, “Corrosion Inhibitors for Steel in
Concrete,” International Congress on Advanced Materials,
Keynote Lecture, Materials Week, Munich, Germany.
Elsner, B.; Buchler, M.; and Bohni, H., 1997, “Corrosion
Inhibitors for Steel in Concrete,” Proceedings of EUROCORR, Trondheim, Norway.
Elsner, B.; Buchler, M.; Stadler, F.; and Bohni, H., 1999,
“Migrating Corrosion Inhibitor Blend for Reinforced
Concrete,” Corrosion, NACE, V. 55, No. 12.
Emmons, P. H., 1993, Concrete Repair and Maintenance
Illustrated: Problem Analysis, Repair Strategy, Techniques,
R. S. Means Co., Kingston, MA, 300 pp.
Federal Highway Administration (FHWA), 2008, “Use and
Inspection of Adhesive Anchors in Federal-Aid Projects,”
Technical Advisory Committee (TA) 5140.30, Oct., 1 p.
Fowler, D. W., and Whitney, D. W., 2011, “Long Term
Performance of Polymer Concrete for Bridge Decks,”
NCHRP Synthesis 423, TRB, Washington, DC.
Hindo, K. R., 1990, “In-Place Bond Testing and Surface
Preparation of Concrete,” Concrete International, V. 12, No.
4, Apr., pp. 46-48.
Holland, T. C., 1987, “Working with Silica-Fume
Concrete,” Concrete Construction, V. 32, No. 3, pp., Mar.,
pp. 261-266.
Holland, T. C., and Gutschow, R. A., 1987, “Erosion
Resistance with Silica-Fume Concrete,” Concrete International, V. 9, No. 3, Mar., pp. 32-40.
Jones, G.; Lambert, P.; and Wood, I., 1999, “Preventing
an Achilles Heel,” Concrete Engineering International, V. 2,
No. 7, Oct., pp. 59-61.
Kosmatka, S. H., 1994, “Bleeding,” Significance of Tests
and Properties of Concrete ad Concrete-Making Materials,
ASTM STP 169C, P. Klieger and J. Lamond, eds., ASTM,
West Conshohocken, PA, pp. 88-111.
American Concrete Institute – Copyrighted © Material – www.concrete.org
70
GUIDE TO CONCRETE REPAIR (ACI 546R-14)
Kuhlmann, L. A., 1984, “The Effect of Cure Time on
Chloride Permeability of Latex-Modified Concrete,” Dow
Chemical Co., Midland, MI.
Kuhlmann, L. A., 1990, “Test Method for Measuring the
Bond Strength of Latex Modified Concrete and Mortar,” ACI
Materials Journal, V. 87, No. 4, July-Aug., pp. 387-394.
Lerch, W., 1957, “Plastic Shrinkage,” ACI Journal
Proceedings, V. 53, Feb, pp. 797-802.
McDonald, J. E., 1987, “Rehabilitation of Navigation
Lock Walls: Case Histories,” Technical Report REMR-CS13, USACE, Vicksburg, MS, Apr., 288 pp.
McDonald, J. E., 1989, “Evaluation of Vinylester Resin
for Anchor Embedment in Concrete,” Technical Report
REMR-CS-20, USACE, Vicksburg, MS, 53 pp.
McDonald, J. E.; Vaysburd, A. M.; Emmons, P. H.; Poston,
R. W.; and Kesner, K. E., 2002, “Selecting Durable Repair
Materials: Performance Criteria—Summary,” Concrete
International, V. 24, No. 1, Jan., pp. 37-44.
McDonald, W. E., 1998, “Evaluation of Grouting Materials for Anchor Embedments in Hardened Concrete,” Technical Report REMR-CS-56, USACE, Vicksburg, MS, Feb.,
164 pp.
Mietz, J.; Elsener, B.; and Polder, R., 1997, “Corrosion
of Reinforcement in Concrete—Monitoring, Prevention and
Rehabilitation,” Publication No. 25, European Federation of
Corrosion (EUROCORR), 64 pp.
National Transportation Safety Board (NTSB), 2007,
“Ceiling Collapse in the Interstate 90 Connector Tunnel,
Boston, Massachusetts, July 10, 2006,” Accident Report
NTSB/HAR-07/02, Washington, DC, July, 120 pp.
PCA, 1995, “Painting Concrete,” PCA IS134, Portland
Cement Association, Skokie, IL, 8 pp.
PCA, 1996, “Resurfacing Concrete Floors,” PCA IS144,
Portland Cement Association, Skokie, IL, 8 pp.
PCA, 1997, “Effects of Substances on Concrete and Guide
to Protective Treatments,” PCA IS001, Portland Cement
Association, Skokie, IL, 36 pp.
Popovic, P. L., 1998, “Durable Repairs for Corrosion
Damaged Concrete,” Proceedings of ICRI Workshop,
Houston, TX.
Project Profile, 1993, “Damaged Bridge Girders Restored,”
Concrete Repair Bulletin, V. 6, No. 4, pp. 23-24.
PTI/ICRI, 2012, “Guide for Evaluation and Repair of
Unbonded Post-Tensioned Concrete Structures,” PTI
DC-80.3-12/ICRI 320.6, Farmington Hills, MI, 54 pp.
Schokker, A. J., 2010, The Sustainable Concrete Guide
– Strategies and Examples, U.S. Green Concrete Council,
Farmington Hills, MI, 89 pp.
Sprinkel, M. M., 1998, “Very-Early-Strength Latex-Modified Concrete Overlay,” TAR 99-TAR3, Virginia Transportation Research Council, Charlottesville, VA, 13 pp.
Sprinkel, M. M., 2011, “Rapid Concrete Bridge Deck
Overlays,” Frontiers in the Use of Polymers in Concrete,
SP-278, M. Reda Taha, ed., American Concrete Institute, Farmington Hills, MI, pp. 1-10. (CD-ROM) DOI:
10.14359/51682508
Thomas, M. D. A.; Fournier, B.; and Folliard, K. J.,
2004, “Protocol for Selecting ASR-Affected Structures
for Lithium Treatment, Report No. FHWA-HRT-04-113,
Federal Highway Transportation Administration (FHWA),
Washington, DC, 23 pp.
Thomas, M. D. A.; Fournier, B.; Folliard, K. J.; Ideker, J.
H.; and Resendez, Y., 2007, “The Use of Lithium to Prevent
or Mitigate Alkali-Silica Reaction in Concrete Pavements
and Structures,” Publication No. FHWA-06-133, Federal
Highway Transportation Administration (FHWA), Washington, DC, 50 pp.
Transportation Research Board, 2001, “Evaluation of
Penetrating Corrosion Inhibitor System,” Ninth Maintenance Management Conference Proceedings 23, Transportation Research Board, Washington, DC, pp. 127-135.
Trout, J., 2006, Epoxy Injection in Construction, second
edition, Hanley-Wood, 85 pp.
Troxell, G. E.; Raphael, J. M.; and Davis, R. E., 1958,
“Long-Time Creep and Shrinkage Tests of Plain and Reinforced Concrete,” ASTM Proceedings, V. 58, pp. 1101-1120.
U.S. Army Corps of Engineers, (USACE), 1989, “Test
Method For Determining The Resistance Of Freshly Mixed
Concrete To Washing Out In Water,” Handbook for Concrete
and Cement, CRD-C 61-89, USACE, Washington, DC, 3 pp.
U.S. Army Corps of Engineers (USACE), 1993, “Standard Specification for Packaged, Dry, Hydraulic-Cement
Grout (Nonshrink),” Handbook for Concrete and Cement,
CRD C621-93, USACE, Concrete Research Division,
Washington, DC, Mar.
U.S. Army Corps of Engineers (USACE), 1995a, “Evaluation and Repair of Concrete Structures,” Engineer Manual,
EM 1110-2-2002, U. S. Army Corps of Engineers, June,
Washington, DC.
U.S. Army Corps of Engineers (USACE), 1995b,
“Chemical Grouting,” Engineer Manual, EM 1110-1-3500,
USACE, Washington, DC, Jan.
U.S. Army Corps of Engineers, (USACE), 2006, “Specification for Antiwashout Admixtures for Concrete,” CRD-C
661, USACE, Washington, DC, Mar., 15 pp.
U.S. Army Corps of Engineers, (USACE), 2009, “Concrete
Rehabilitation for Civil Works,” UFGS-03 01 32, USACE,
Washington, DC, Nov., 73 pp.
Virginia Transportation Research Council, 2001, “Evaluation of High Performance Concrete Overlays Placed on
Bridges and Pavements in Virginia,” VTRC 01-R1-R3RB.
Warner, J., 1984, “Selecting Repair Materials,” Concrete
Construction, V. 29, No. 10, Oct., pp. 865-871.
American Concrete Institute – Copyrighted © Material – www.concrete.org
As ACI begins its second century of advancing concrete knowledge, its original chartered purpose
remains “to provide a comradeship in finding the best ways to do concrete work of all kinds and in
spreading knowledge.” In keeping with this purpose, ACI supports the following activities:
· Technical committees that produce consensus reports, guides, specifications, and codes.
· Spring and fall conventions to facilitate the work of its committees.
· Educational seminars that disseminate reliable information on concrete.
· Certification programs for personnel employed within the concrete industry.
· Student programs such as scholarships, internships, and competitions.
· Sponsoring and co-sponsoring international conferences and symposia.
· Formal coordination with several international concrete related societies.
· Periodicals: the ACI Structural Journal, Materials Journal, and Concrete International.
Benefits of membership include a subscription to Concrete International and to an ACI Journal. ACI
members receive discounts of up to 40% on all ACI products and services, including documents, seminars
and convention registration fees.
As a member of ACI, you join thousands of practitioners and professionals worldwide who share
a commitment to maintain the highest industry standards for concrete technology, construction,
and practices. In addition, ACI chapters provide opportunities for interaction of professionals and
practitioners at a local level.
American Concrete Institute
38800 Country Club Drive
Farmington Hills, MI 48331
Phone: +1.248.848.3700
Fax: +1.248.848.3701
www.concrete.org
38800 Country Club Drive
Farmington Hills, MI 48331 USA
+1.248.848.3700
www.concrete.org
The American Concrete Institute (ACI) is a leading authority and resource
worldwide for the development and distribution of consensus-based
standards and technical resources, educational programs, and certifications
for individuals and organizations involved in concrete design, construction,
and materials, who share a commitment to pursuing the best use of concrete.
Individuals interested in the activities of ACI are encouraged to explore the
ACI website for membership opportunities, committee activities, and a wide
variety of concrete resources. As a volunteer member-driven organization,
ACI invites partnerships and welcomes all concrete professionals who wish to
be part of a respected, connected, social group that provides an opportunity
for professional growth, networking and enjoyment.
9
780870
319334